chore: re-sync context adapters with upstream root

Derived adapters drifted from canonical root .context/AGENT.md after
the pgvector default change landed upstream. Pure regeneration via
scripts/context-sync.sh, no manual edits. Required to make task check
pass before the feature commits on this branch.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.context/system-prompt.txt

@@ -41,9 +41,6 @@ These rules apply to every task across every project, regardless of harness.
 4. **Goal-driven execution.** Define clear success criteria up front for every task.
    Loop — implement, verify, refine — until those criteria are met. Don't claim
    completion without evidence (tests pass, command output, observed behavior).
-5. **Branch-per-task for multi-agent repos.** When another agent may be active on
-   the same repo, create a branch (`agent/<description>`), commit there, and open a
-   PR. Do not merge without explicit instruction from Mathias.
 
 ## Default stack
 
@@ -54,7 +51,7 @@ These rules apply to every task across every project, regardless of harness.
 | Build | Task (taskfile.dev) | Make | — |
 | Containers | Docker Compose (dev), k3s (prod) | — | — |
 | DB | PostgreSQL + sqlc | SQLite | — |
-| Search | Qdrant (vector), BM25 | — | — |
+| Search | pgvector (vector), BM25 | Qdrant (when >1M vectors or hybrid retrieval) | — |
 | Logging | slog (structured) | — | — |
 | Testing | Table-driven, testify | — | — |
 
@@ -76,7 +73,7 @@ Three machines on Tailscale:
 
 | Machine | Role | Key specs |
 |---------|------|-----------|
-| koala | GPU inference, heavy compute | RTX 5070, runs llama-swap, Qdrant |
+| koala | GPU inference, heavy compute | RTX 5070, runs k3s + llama-swap + shared postgres18/pgvector |
 | iguana | Services, builds | M2 Ultra Mac |
 | flamingo | Daily driver, edge | Mac mini, ~/dev is here |