feat: Add ROI tracking with discovery_tokens for observations and session summaries (#111)

* feat: Add discovery_tokens for ROI tracking in observations and session summaries

- Introduced `discovery_tokens` column in `observations` and `session_summaries` tables to track token costs associated with discovering and creating each observation and summary.
- Updated relevant services and hooks to calculate and display ROI metrics based on discovery tokens.
- Enhanced context economics reporting to include savings from reusing previous observations.
- Implemented migration to ensure the new column is added to existing tables.
- Adjusted data models and sync processes to accommodate the new `discovery_tokens` field.

* refactor: streamline context hook by removing unused functions and updating terminology

- Removed the estimateTokens and getObservations helper functions as they were not utilized.
- Updated the legend and output messages to replace "discovery" with "work" for clarity.
- Changed the emoji representation for different observation types to better reflect their purpose.
- Enhanced output formatting for improved readability and understanding of token usage.

* Refactor user-message-hook and context-hook for improved clarity and functionality

- Updated user-message-hook.js to enhance error messaging and improve variable naming for clarity.
- Modified context-hook.ts to include a new column key section, improved context index instructions, and added emoji icons for observation types.
- Adjusted footer messages in context-hook.ts to emphasize token savings and access to past research.
- Changed user-message-hook.ts to update the feedback and support message for clarity.

* fix: Critical ROI tracking fixes from PR review

Addresses critical findings from PR #111 review:

1. **Fixed incorrect discovery token calculation** (src/services/worker/SDKAgent.ts)
   - Changed from passing cumulative total to per-response delta
   - Now correctly tracks token cost for each observation/summary
   - Captures token state before/after response processing
   - Prevents all observations getting inflated cumulative values

2. **Fixed schema version mismatch** (src/services/sqlite/SessionStore.ts)
   - Changed ensureDiscoveryTokensColumn() from version 11 to version 7
   - Now matches migration007 definition in migrations.ts
   - Ensures consistent version tracking across migration system

These fixes ensure ROI metrics accurately reflect token costs.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/services/sqlite/SessionSearch.ts

@@ -264,6 +264,7 @@ export class SessionSearch {
     const sql = `
       SELECT
         o.*,
+        o.discovery_tokens,
         observations_fts.rank as rank
       FROM observations o
       JOIN observations_fts ON o.id = observations_fts.rowid
@@ -326,6 +327,7 @@ export class SessionSearch {
     const sql = `
       SELECT
         s.*,
+        s.discovery_tokens,
         session_summaries_fts.rank as rank
       FROM session_summaries s
       JOIN session_summaries_fts ON s.id = session_summaries_fts.rowid
@@ -368,7 +370,7 @@ export class SessionSearch {
     const orderClause = this.buildOrderClause(orderBy, false);
 
     const sql = `
-      SELECT o.*
+      SELECT o.*, o.discovery_tokens
       FROM observations o
       WHERE ${filterClause}
       ${orderClause}
@@ -396,7 +398,7 @@ export class SessionSearch {
     const orderClause = this.buildOrderClause(orderBy, false);
 
     const observationsSql = `
-      SELECT o.*
+      SELECT o.*, o.discovery_tokens
       FROM observations o
       WHERE ${filterClause}
       ${orderClause}
@@ -440,7 +442,7 @@ export class SessionSearch {
     sessionParams.push(`%${filePath}%`, `%${filePath}%`);
 
     const sessionsSql = `
-      SELECT s.*
+      SELECT s.*, s.discovery_tokens
       FROM session_summaries s
       WHERE ${baseConditions.join(' AND ')}
       ORDER BY s.created_at_epoch DESC
@@ -470,7 +472,7 @@ export class SessionSearch {
     const orderClause = this.buildOrderClause(orderBy, false);
 
     const sql = `
-      SELECT o.*
+      SELECT o.*, o.discovery_tokens
       FROM observations o
       WHERE ${filterClause}
       ${orderClause}