refactor: replace context_token_budget with model context_window for context trimming

The per-bot context_token_budget column was unused (no frontend UI) and
has been removed. Context trimming now derives the budget from the chat
model's context_window setting, which is already configured per model.

internal/db/sqlc/conversations.sql.go

@@ -511,7 +511,7 @@ WITH updated AS (
   SET display_name = $1,
       updated_at = now()
   WHERE bots.id = $2
-  RETURNING id, owner_user_id, display_name, avatar_url, timezone, is_active, status, language, reasoning_enabled, reasoning_effort, chat_model_id, search_provider_id, memory_provider_id, heartbeat_enabled, heartbeat_interval, heartbeat_prompt, heartbeat_model_id, compaction_enabled, compaction_threshold, compaction_ratio, compaction_model_id, title_model_id, image_model_id, discuss_probe_model_id, tts_model_id, browser_context_id, context_token_budget, persist_full_tool_results, metadata, created_at, updated_at, acl_default_effect
+  RETURNING id, owner_user_id, display_name, avatar_url, timezone, is_active, status, language, reasoning_enabled, reasoning_effort, chat_model_id, search_provider_id, memory_provider_id, heartbeat_enabled, heartbeat_interval, heartbeat_prompt, heartbeat_model_id, compaction_enabled, compaction_threshold, compaction_ratio, compaction_model_id, title_model_id, image_model_id, discuss_probe_model_id, tts_model_id, browser_context_id, persist_full_tool_results, metadata, created_at, updated_at, acl_default_effect
 )
 SELECT
   updated.id AS id,

internal/db/sqlc/models.go

@@ -35,7 +35,6 @@ type Bot struct {
 	DiscussProbeModelID    pgtype.UUID        `json:"discuss_probe_model_id"`
 	TtsModelID             pgtype.UUID        `json:"tts_model_id"`
 	BrowserContextID       pgtype.UUID        `json:"browser_context_id"`
-	ContextTokenBudget     pgtype.Int4        `json:"context_token_budget"`
 	PersistFullToolResults bool               `json:"persist_full_tool_results"`
 	Metadata               []byte             `json:"metadata"`
 	CreatedAt              pgtype.Timestamptz `json:"created_at"`

internal/db/sqlc/settings.sql.go

@@ -31,7 +31,6 @@ SET language = 'auto',
     memory_provider_id = NULL,
     tts_model_id = NULL,
     browser_context_id = NULL,
-    context_token_budget = NULL,
     persist_full_tool_results = false,
     updated_at = now()
 WHERE id = $1
@@ -64,7 +63,6 @@ SELECT
   image_models.id AS image_model_id,
   tts_models.id AS tts_model_id,
   browser_contexts.id AS browser_context_id,
-  bots.context_token_budget,
   bots.persist_full_tool_results
 FROM bots
 LEFT JOIN models AS chat_models ON chat_models.id = bots.chat_model_id
@@ -100,7 +98,6 @@ type GetSettingsByBotIDRow struct {
 	ImageModelID           pgtype.UUID `json:"image_model_id"`
 	TtsModelID             pgtype.UUID `json:"tts_model_id"`
 	BrowserContextID       pgtype.UUID `json:"browser_context_id"`
-	ContextTokenBudget     pgtype.Int4 `json:"context_token_budget"`
 	PersistFullToolResults bool        `json:"persist_full_tool_results"`
 }
 
@@ -128,7 +125,6 @@ func (q *Queries) GetSettingsByBotID(ctx context.Context, id pgtype.UUID) (GetSe
 		&i.ImageModelID,
 		&i.TtsModelID,
 		&i.BrowserContextID,
-		&i.ContextTokenBudget,
 		&i.PersistFullToolResults,
 	)
 	return i, err
@@ -156,11 +152,10 @@ WITH updated AS (
       image_model_id = COALESCE($17::uuid, bots.image_model_id),
       tts_model_id = COALESCE($18::uuid, bots.tts_model_id),
       browser_context_id = COALESCE($19::uuid, bots.browser_context_id),
-      context_token_budget = COALESCE($20::integer, bots.context_token_budget),
-      persist_full_tool_results = $21,
+      persist_full_tool_results = $20,
       updated_at = now()
-  WHERE bots.id = $22
-  RETURNING bots.id, bots.language, bots.reasoning_enabled, bots.reasoning_effort, bots.heartbeat_enabled, bots.heartbeat_interval, bots.heartbeat_prompt, bots.compaction_enabled, bots.compaction_threshold, bots.compaction_ratio, bots.timezone, bots.chat_model_id, bots.heartbeat_model_id, bots.compaction_model_id, bots.title_model_id, bots.image_model_id, bots.search_provider_id, bots.memory_provider_id, bots.tts_model_id, bots.browser_context_id, bots.context_token_budget, bots.persist_full_tool_results
+  WHERE bots.id = $21
+  RETURNING bots.id, bots.language, bots.reasoning_enabled, bots.reasoning_effort, bots.heartbeat_enabled, bots.heartbeat_interval, bots.heartbeat_prompt, bots.compaction_enabled, bots.compaction_threshold, bots.compaction_ratio, bots.timezone, bots.chat_model_id, bots.heartbeat_model_id, bots.compaction_model_id, bots.title_model_id, bots.image_model_id, bots.search_provider_id, bots.memory_provider_id, bots.tts_model_id, bots.browser_context_id, bots.persist_full_tool_results
 )
 SELECT
   updated.id AS bot_id,
@@ -183,7 +178,6 @@ SELECT
   image_models.id AS image_model_id,
   tts_models.id AS tts_model_id,
   browser_contexts.id AS browser_context_id,
-  updated.context_token_budget,
   updated.persist_full_tool_results
 FROM updated
 LEFT JOIN models AS chat_models ON chat_models.id = updated.chat_model_id
@@ -217,7 +211,6 @@ type UpsertBotSettingsParams struct {
 	ImageModelID           pgtype.UUID `json:"image_model_id"`
 	TtsModelID             pgtype.UUID `json:"tts_model_id"`
 	BrowserContextID       pgtype.UUID `json:"browser_context_id"`
-	ContextTokenBudget     pgtype.Int4 `json:"context_token_budget"`
 	PersistFullToolResults bool        `json:"persist_full_tool_results"`
 	ID                     pgtype.UUID `json:"id"`
 }
@@ -243,7 +236,6 @@ type UpsertBotSettingsRow struct {
 	ImageModelID           pgtype.UUID `json:"image_model_id"`
 	TtsModelID             pgtype.UUID `json:"tts_model_id"`
 	BrowserContextID       pgtype.UUID `json:"browser_context_id"`
-	ContextTokenBudget     pgtype.Int4 `json:"context_token_budget"`
 	PersistFullToolResults bool        `json:"persist_full_tool_results"`
 }
 
@@ -268,7 +260,6 @@ func (q *Queries) UpsertBotSettings(ctx context.Context, arg UpsertBotSettingsPa
 		arg.ImageModelID,
 		arg.TtsModelID,
 		arg.BrowserContextID,
-		arg.ContextTokenBudget,
 		arg.PersistFullToolResults,
 		arg.ID,
 	)
@@ -294,7 +285,6 @@ func (q *Queries) UpsertBotSettings(ctx context.Context, arg UpsertBotSettingsPa
 		&i.ImageModelID,
 		&i.TtsModelID,
 		&i.BrowserContextID,
-		&i.ContextTokenBudget,
 		&i.PersistFullToolResults,
 	)
 	return i, err