fix: make migration 17 fully idempotent for databases in intermediate states (#481)

* fix: make migration 17 idempotent and standardize column names

Migration 17 renamed columns from sdk_session_id to memory_session_id,
but the migration wasn't fully idempotent - it could fail on databases
in intermediate states. This caused errors like:
- "no such column: sdk_session_id" (when columns already renamed)
- "table observations has no column named memory_session_id" (when not renamed)

Changes:
- Rewrite renameSessionIdColumns() to check each table individually
- Use safeRenameColumn() helper that handles all edge cases gracefully
- Deprecate migration 19 (repair migration) since 17 is now idempotent
- Update maintenance scripts to use memory_session_id column name
- Update test files to use new column names

Fixes column mismatch bug in v8.2.6+

* Merge origin/main into column-mismatch

---------

Co-authored-by: Alex Newman <thedotmack@gmail.com>

scripts/investigate-timestamps.ts

@@ -36,7 +36,7 @@ function main() {
     const dec24End = 1735113600000;   // Dec 25 00:00 PST
 
     const dec24Obs = db.query(`
-      SELECT id, sdk_session_id, created_at_epoch, title
+      SELECT id, memory_session_id, created_at_epoch, title
       FROM observations
       WHERE created_at_epoch >= ${dec24Start}
         AND created_at_epoch < ${dec24End}
@@ -59,7 +59,7 @@ function main() {
     const dec21Start = 1734768000000; // Dec 21 00:00 PST
 
     const oldObs = db.query(`
-      SELECT id, sdk_session_id, created_at_epoch, title
+      SELECT id, memory_session_id, created_at_epoch, title
       FROM observations
       WHERE created_at_epoch >= ${dec17Start}
         AND created_at_epoch < ${dec21Start}