chore(.agents): keep lean — remove default mode files, no modes list

.agents/ is an override layer. Default modes (ask/build/autonomous)
and default skills come from SF's built-in config. Project files only
exist when overriding or adding something project-specific.

- Remove modes/ask.md, modes/build.md, modes/autonomous.md (defaults)
- Remove enabled.modes from manifest (nothing project-defined)
- Policies and skills stay: they are project-specific overrides

To override a mode or skill, add a file with the same name.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.agents/manifest.yaml

@@ -11,10 +11,7 @@ defaults:
   policy: default-safe
 
 enabled:
-  modes:
-    - ask
-    - build
-    - autonomous
+  # modes: not listed — no project overrides; SF built-in modes (ask/build/autonomous) apply
   policies:
     - default-safe
     - yolo

.agents/modes/ask.md

@@ -1,39 +0,0 @@
----
-id: ask
-title: Ask
-policy: default-safe
-enableSkills: []
-disableSkills: []
-includeSnippets:
-  - style
-  - principles
-  - non-goals
-toolIntent:
-  allow:
-    - read
-    - search
-    - web_fetch
-  deny:
-    - write
-    - exec_command
-    - git_commit
-    - git_push
----
-
-# Ask Mode
-
-Read-only investigation. Answer questions about the codebase, propose
-plans, but **make no changes**.
-
-Use this mode when:
-
-- The user is exploring or trying to understand something.
-- A plan needs review before implementation.
-- The right next step is unclear and probing the code base will help.
-
-Switch to Build (Shift+Tab) when the user is ready for the agent to
-make changes.
-
-This mode's policy denies writes, command execution, and git mutation.
-If a task requires any of those, surface that fact rather than
-attempting and failing.

.agents/modes/autonomous.md

@@ -1,67 +0,0 @@
----
-id: autonomous
-title: Autonomous
-policy: default-safe
-enableSkills:
-  - forge-autonomous-runtime
-disableSkills: []
-includeSnippets:
-  - style
-  - principles
-  - non-goals
-toolIntent:
-  allow:
-    - read
-    - search
-    - web_fetch
-    - write
-    - exec_command
-    - git_commit
-  deny:
-    - git_push_force
-    - rm_rf
-    - drop_table
----
-
-# Autonomous Mode
-
-Long-horizon unattended execution. SF drives the full UOK dispatch
-loop: milestone → slice → task → commit, without human confirmation
-per unit. The deterministic controller (not the LLM) reads `sf.db`
-and decides what to dispatch next.
-
-**Entry points:**
-
-- `sf run --autonomous` (CLI)
-- `sf headless next` / `sf headless autonomous` (machine surface)
-- TUI: enable via `/autonomous` or the autonomous panel
-
-**Differences from Build:**
-
-- No per-unit human confirmation gate.
-- Each task unit gets a **fresh agent context** — no accumulated state
-  between units.
-- Budget limits enforced: turn cap and token cap per unit.
-- The 120 s bash default timeout is critical here — without it a
-  single hanging command consumes the entire autonomous run budget.
-- Bash tool has a 120 s default timeout (configurable via
-  `settings.json → bash.defaultTimeoutSeconds`).
-- Recovery and runaway-guard are active; stuck units are retried or
-  abandoned automatically.
-
-**What does NOT change in this mode:**
-
-- Path deny rules and redactions from the active policy still apply.
-- Secrets are never written to commits or logs.
-- Destructive operations (`rm -rf`, `git push --force`, `drop_table`)
-  are still denied.
-
-**When to use:**
-
-Use autonomous mode when the milestone/slice plan is stable, tests are
-present, and the work is low-blast-radius. Use Build mode when you
-want to review changes interactively or the task is novel/risky.
-
-The YOLO flag (`Ctrl+Y` / `/mode yolo`) can be layered on top of
-Build or Autonomous to drop the remaining confirmation gates entirely.
-It is a flag — not a mode — and does not appear as a Shift+Tab stop.

.agents/modes/build.md

@@ -1,43 +0,0 @@
----
-id: build
-title: Build
-policy: default-safe
-enableSkills: []
-disableSkills: []
-includeSnippets:
-  - style
-  - principles
-  - non-goals
-toolIntent:
-  allow:
-    - read
-    - search
-    - web_fetch
-    - write
-    - exec_command
-    - git_commit
-  deny:
-    - git_push_force
-    - rm_rf
-    - drop_table
----
-
-# Build Mode
-
-Active development. Make changes, run tests, commit.
-
-Confirmations are required for destructive operations per the
-default-safe policy (rm -rf, git push --force, git reset --hard,
-drop_table, etc.). Toggle the YOLO flag (Ctrl+Y) to drop those
-confirmations — that's a flag on Build, not a separate mode.
-
-In this mode the agent is expected to:
-
-- Run tests before committing.
-- Group related changes in a single commit; don't bundle unrelated
-  work.
-- Use Git history as the rationale store — clear commit messages,
-  rationale in the body, link to ADRs when relevant.
-- Update tests when changing behaviour.
-- Promote durable decisions to `docs/adr/` rather than burying them
-  in commit messages.