refactor(agents): collapse per-task agents into flagship skills - #2995

Thirteen agent packages are gone: code, routing, blender, sd, emr, analyst,
browser, docqa, doc-search, fileio, summarize, jira, docker. Their capability
now comes from the flagship agent's tool surface driven by a SKILL.md, which is
where new capability belongs — a skill is a markdown file, an agent was a wheel
with a manifest, CI, docs, and a publish slot.

Most of them were never reachable: only email and gaia have a daemon sidecar
spec or a launchable TUI catalog row, so the rest showed as "not published on
the Agent Hub yet" and could not be installed at all. Several defined zero tools
of their own and consisted entirely of a system prompt already covered by the
flagship's 66 registered tools.

Two new skills carry forward the prose worth keeping: file-ops (from fileio) and
summarize (the style tables and fold-forward chunking from summarize's
prompts.py). data-explore, research-report and document-brief already existed
and cover analyst, browser and docqa/doc-search.

Also removed as dead weight: the jira/summarize/docker standalone apps, the
Blender MCP client/server pair, the Docker MCP server, the MCP bridge's
jira/blender/summarize surfaces and the multipart upload path that only the
summarize endpoint used, the bpy extra, and the blender/jira/docker Claude
specialist definitions.

Behaviour changes a user can see:
- `gaia analyze|browse|summarize|blender|sd|jira|docker` and `gaia mcp docker`
  are gone, as are the gaia-code and gaia-emr console scripts.
- `gaia api` exposes no models: AGENT_MODELS held one entry, the routing agent,
  which routed to the code agent.
- hello-world, word-count and connectors-demo stay as teaching templates and are
  no longer catalog agents.

Jira and Docker return as connectors, scoped in amd#2989 and amd#2990.

The starter-pack guard checks tools_required against the tools mixins
register plus a short whitelist of the tools ChatAgent registers inline. The
whitelist was missing request_user_input, so the new file-ops skill failed the
guard for declaring a tool the flagship really does register — asking the user
before a destructive write is the whole point of that skill.

Verified the same way as the rest of the list: the `def` must exist in the chat
agent's source, so a rename drops the name instead of silently passing.

`execute_python_file` runs a .py file in a subprocess — arbitrary code
execution — but it was the one dangerous tool missing from the confirmation
gate. `run_shell_command` sits behind both the gate AND a read-only command
allowlist; this had neither, so it was the weakest link in the set.

It mattered little while the OpenAI-compatible server exposed nothing. Now that
it serves the flagship, an unattended caller reaches a 61-tool agent, so the gap
closes here. Verified: the tool is refused and the file does not run.

Also from review of this branch:

- Dropped `python-multipart` from core install_requires. It was there because
  the MCP bridge imported it at module load to parse multipart uploads for the
  summarize endpoint; that endpoint and the import are gone, and nothing else
  under src/ imports it. It stays in the `api` and `ui` extras, which do.
- Removed `send_sse_headers` and `stream_sse` from the bridge — the deleted
  summarize endpoint was their only caller.
- Corrected an ApiAgent docstring that claimed `GaiaAgent -> gaia`; the default
  it documents would produce `gaia-gaia`, and the flagship is served under the
  `gaia` key in AGENT_MODELS instead.

The one that mattered: deleting the browse/analyze branch left its trailing
`agent.close()` behind, stitched into the chat branch's cleanup one level too
deep — inside `except Exception: pass`. Neither ChatAgent nor the base Agent
has a `close()`, and the `hasattr` guard that used to protect it went with the
deleted block, so a `gaia chat` run where `stop_watching()` raised would have
turned a graceful exit into an AttributeError escaping the `finally` and hiding
the original error. Also swept the tree for that whole bug class (a statement
stranded after `pass`, an unreachable statement after `return`) — nothing else.

The summarize skill told the model to pass `summary_type` values the tool
rejects. `summarize_document` validates against exactly brief/detailed/bullets,
while the skill named `executive`, `action_items`, `participants` and friends in
backticks — inherited from the deleted agent, which validated those itself. The
most natural transcript ask, "what were the action items", would have returned
an error instead of a summary. The style vocabulary stays as prose guidance; the
skill now says which three values are real.

`GET /v1/models` built a full agent just to read two integers off it. That was
cheap when the entry was the routing agent and expensive now that it is the
flagship, whose constructor opens RAG, scratchpad and memory handles and an HTTP
session — on an endpoint clients poll at startup. It now checks the class and
only instantiates an actual ApiAgent: 291ms first call, 2ms after, no handles.

Smaller: `gaia init --profile` advertised `code` in argparse choices after the
profile was deleted; the `sd` profile's quick-start printed `gaia sd`, a command
this branch removed; `gaia download`'s epilog demoed `--agent code`; a
`wait_for_user` helper whose only caller was a Blender demo; scripts/jira_smoke.py
imported two deleted modules; and assorted docstrings, menu strings and plan-doc
links still pointed at agents that no longer exist.