feat: add compaction ratio setting to control partial context compaction

Allow users to configure what percentage of older messages to compact,
keeping the most recent portion intact. Default ratio is 80%, meaning
the oldest 80% of uncompacted messages are summarized while the newest
20% remain as-is for full-fidelity context.

db/migrations/0001_init.up.sql

@@ -174,6 +174,7 @@ CREATE TABLE IF NOT EXISTS bots (
   heartbeat_model_id UUID REFERENCES models(id) ON DELETE SET NULL,
   compaction_enabled BOOLEAN NOT NULL DEFAULT false,
   compaction_threshold INTEGER NOT NULL DEFAULT 100000,
+  compaction_ratio INTEGER NOT NULL DEFAULT 80,
   compaction_model_id UUID REFERENCES models(id) ON DELETE SET NULL,
   title_model_id UUID REFERENCES models(id) ON DELETE SET NULL,
   tts_model_id UUID REFERENCES tts_models(id) ON DELETE SET NULL,

db/migrations/0052_compaction_ratio.down.sql

@@ -0,0 +1,4 @@
+-- 0052_compaction_ratio (rollback)
+-- Remove compaction_ratio column from bots table.
+
+ALTER TABLE bots DROP COLUMN IF EXISTS compaction_ratio;

db/migrations/0052_compaction_ratio.up.sql

@@ -0,0 +1,4 @@
+-- 0052_compaction_ratio
+-- Add compaction_ratio column to bots table for controlling what percentage of messages to compact.
+
+ALTER TABLE bots ADD COLUMN IF NOT EXISTS compaction_ratio INTEGER NOT NULL DEFAULT 80;