navi-web: make the batch shape the schema, drop Brave ...

Every recorded web_search and web_view call in production carried a scalar
(20 of 20, 8 of 8), including sessions where three searches on one topic went
out one after another. The recommendation was already written in three
places — the parameter description, the tool docstring and the server's
summary line — so prose was not the problem: `str | list[str]` renders as
`anyOf: [string, array]`, and the model took the first branch.

The parameter is now a pure array with minItems/maxItems and an examples
entry. A BeforeValidator folds a bare "query": "…" into a one-item list, so a
laxer caller still works; the cap rides in json_schema_extra rather than
pydantic's max_length, so four queries reach the code that runs three and
names the rest instead of failing validation.

Brave is gone on both paths: the keyed Search API (signup answers 403, so a
third backend that can never be enabled) and the ddgs engine of the same name,
which answers nothing from this host. The chain is SearXNG -> ddgs.

The persona's parallelism rule now separates "several items in one call" from
"several calls in one message" — it used to read "when the profile allows
parallel tool calls", which the model could only read as "not here".

Migrate web tools (web_search, web_view, http_request) to navi-web MCP server ...

New MCP server: mcp-servers/navi-web/
- app/search.py    — SearXNG primary, DDG fallback, Brave tertiary
- app/browse.py    — Playwright headless browser page extraction
- app/request.py   — httpx raw HTTP requests
- app/mcp_server.py — FastMCP entry point with stdio transport
- pyproject.toml   — deps: mcp, httpx, ddgs, playwright, pydantic

Changes:
- Added "navi-web" block to mcp_servers.json (stdio transport)
- Removed web_search, web_view, http_request from built-in registry
- Removed them from navi/tools/__init__.py
- Removed them from enabled_tools / subagent_tools in all profiles
- Added "navi-web": ["search", "browse", "request"] to mcp_servers
  in all profiles (developer, secretary, server_admin, tool_developer,
  modeler_3d, discuss)

Tests: 240 passed.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>