feat(coach): lay down the reasoning, trail and memory contract

Add the shared contract the reasoning release builds on, with no change
to how a turn runs today.

- Schema: operator reasoning controls on app_settings (0376), the
  encrypted trail text on coach_messages (0377), and source,
  last_used_at and source_message_id on coach_facts (0378).
- Provider contract: CompletionParams.reasoning and onReasoning,
  CompletionResult.reasoning and providerState, AiMessage.providerState.
- Reasoning levels, thinking budgets and the background-job table in
  src/lib/ai/reasoning/levels.ts; coachPrefsJson.reasoning, absent
  meaning medium, salvaged field by field like every other pref.
- Stream: activity, memoryNote and planProposal frames, done.stop and
  done.withheldResults, result.interim, a compare chart kind, eight
  table refs, three more clarification kinds with an assumed choice,
  the change_assumption chip, and assumptions, activity, stop,
  memoryNote and planProposal on the provenance. Zod mirror, type
  parity and the native-client key rule cover every new frame.
- Chat request: memoryDecision and planDecision, parsed and not yet
  acted on.
- Stub contracts for the memory functions and the activity recorder,
  inert until their implementations land.
- Backup, restore and rotation carry the new columns; a fact's message
  reference is resolved against the restored messages like its
  conversation reference.
- Message keys for the trail, memory, plans, assumptions, replies,
  interim tables, comparison charts and reasoning settings in all seven
  locales, each reachable from a catalog and checked both ways.

scripts/rotate-encryption-key.ts

@@ -462,8 +462,8 @@ async function main() {
   }
 
   // ───── Coach (Bytes columns) ─────
-  // "encryptedContent" "resultsEncrypted" "summaryEncrypted" "titleEncrypted"
-  // "factEncrypted"
+  // "encryptedContent" "resultsEncrypted" "trailEncrypted" "summaryEncrypted"
+  // "titleEncrypted" "factEncrypted"
   results.push(
     await rotateBytesColumn(
       "CoachMessage",
@@ -480,6 +480,15 @@ async function main() {
       prisma.coachMessage,
     ),
   );
+  // v1.41 — the model text of the turn's trail. NULL on every turn without
+  // one, which `rotateBytesColumn` skips.
+  results.push(
+    await rotateBytesColumn(
+      "CoachMessage",
+      "trailEncrypted",
+      prisma.coachMessage,
+    ),
+  );
   results.push(
     await rotateBytesColumn(
       "CoachConversation",