feat: add session info panel with message count, context usage, cache stats, and skills

Add GET /bots/:bot_id/sessions/:session_id/info API endpoint that returns
per-session message count, latest input token usage with model context window,
aggregated KV cache hit rate, and skills invoked via use_skill tool calls.
Frontend Info tab in the right sidebar now displays this data in a compact
key-value layout with a context usage progress bar and clickable skill links.

internal/db/sqlc/session_info.sql.go

@@ -0,0 +1,105 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.30.0
+// source: session_info.sql
+
+package sqlc
+
+import (
+	"context"
+
+	"github.com/jackc/pgx/v5/pgtype"
+)
+
+const countMessagesBySession = `-- name: CountMessagesBySession :one
+SELECT COUNT(*)::bigint AS message_count
+FROM bot_history_messages
+WHERE session_id = $1
+`
+
+func (q *Queries) CountMessagesBySession(ctx context.Context, sessionID pgtype.UUID) (int64, error) {
+	row := q.db.QueryRow(ctx, countMessagesBySession, sessionID)
+	var message_count int64
+	err := row.Scan(&message_count)
+	return message_count, err
+}
+
+const getLatestAssistantUsage = `-- name: GetLatestAssistantUsage :one
+SELECT
+  COALESCE((m.usage->>'inputTokens')::bigint, 0)::bigint AS input_tokens
+FROM bot_history_messages m
+WHERE m.session_id = $1
+  AND m.role = 'assistant'
+  AND m.usage IS NOT NULL
+ORDER BY m.created_at DESC
+LIMIT 1
+`
+
+func (q *Queries) GetLatestAssistantUsage(ctx context.Context, sessionID pgtype.UUID) (int64, error) {
+	row := q.db.QueryRow(ctx, getLatestAssistantUsage, sessionID)
+	var input_tokens int64
+	err := row.Scan(&input_tokens)
+	return input_tokens, err
+}
+
+const getSessionCacheStats = `-- name: GetSessionCacheStats :one
+SELECT
+  COALESCE(SUM((m.usage->>'inputTokens')::bigint), 0)::bigint AS total_input_tokens,
+  COALESCE(SUM((m.usage->'inputTokenDetails'->>'cacheReadTokens')::bigint), 0)::bigint AS cache_read_tokens,
+  COALESCE(SUM((m.usage->'inputTokenDetails'->>'cacheWriteTokens')::bigint), 0)::bigint AS cache_write_tokens
+FROM bot_history_messages m
+WHERE m.session_id = $1
+  AND m.usage IS NOT NULL
+`
+
+type GetSessionCacheStatsRow struct {
+	TotalInputTokens int64 `json:"total_input_tokens"`
+	CacheReadTokens  int64 `json:"cache_read_tokens"`
+	CacheWriteTokens int64 `json:"cache_write_tokens"`
+}
+
+func (q *Queries) GetSessionCacheStats(ctx context.Context, sessionID pgtype.UUID) (GetSessionCacheStatsRow, error) {
+	row := q.db.QueryRow(ctx, getSessionCacheStats, sessionID)
+	var i GetSessionCacheStatsRow
+	err := row.Scan(&i.TotalInputTokens, &i.CacheReadTokens, &i.CacheWriteTokens)
+	return i, err
+}
+
+const getSessionUsedSkills = `-- name: GetSessionUsedSkills :many
+SELECT DISTINCT
+  (part->'input'->>'skillName')::text AS skill_name
+FROM bot_history_messages m,
+  jsonb_array_elements(
+    CASE WHEN jsonb_typeof(m.content->'content') = 'array'
+         THEN m.content->'content'
+         ELSE '[]'::jsonb
+    END
+  ) AS part
+WHERE m.session_id = $1
+  AND m.role = 'assistant'
+  AND part->>'type' = 'tool-call'
+  AND part->>'toolName' = 'use_skill'
+  AND part->'input'->>'skillName' IS NOT NULL
+  AND part->'input'->>'skillName' != ''
+ORDER BY skill_name
+`
+
+func (q *Queries) GetSessionUsedSkills(ctx context.Context, sessionID pgtype.UUID) ([]string, error) {
+	rows, err := q.db.Query(ctx, getSessionUsedSkills, sessionID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []string
+	for rows.Next() {
+		var skill_name string
+		if err := rows.Scan(&skill_name); err != nil {
+			return nil, err
+		}
+		items = append(items, skill_name)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}