feat(session): persist model tier overrides per session

Store per-session config in SQLite and route /model and /reset through command fast-paths so channel sessions keep independent model selection across reconnects and restarts.

config/default.yaml

@@ -80,6 +80,30 @@ hooks:
   silent:
     - notify
 
+# ── Prompt Assembly ───────────────────────────────────────────────────
+# Tune how much context Flynn loads into the system prompt.
+#
+# prompt:
+#   search_dirs: []
+#   extra_sections: []
+#   context_level: normal  # minimal | normal | detailed | debug
+
+# skills:
+#   # Global installer execution policy.
+#   # disabled: never run installer commands (default)
+#   # enabled: allow command execution only with --execute --confirm
+#   installation_execution: disabled
+#   # Allow shell-based installer runner when --runner shell is requested.
+#   allow_shell_runner: false
+#   # Allowlist command patterns for shell runner (`*` wildcard supported).
+#   # Empty list means no shell commands are allowed.
+#   shell_runner_allowlist: []
+#   # Governance metadata for shell-runner allowlist and rollout decisions.
+#   shell_runner_governance:
+#     owner: "skills-team"               # Required when allow_shell_runner is true
+#     review_cadence_days: 7              # Review `skills rollout-status` at this cadence
+#     promotion_min_success_rate: 0.9     # Rollout threshold for broader enablement
+
 # ── Automation ──────────────────────────────────────────────────────
 # Uncomment and configure any automation sources you need.