feat(mcp): read a working-directory .mcp.json, honor enabled:false, name unmodelled keys; bump v1.1.29

[laohanlinux]

Three commits on top of v1.1.28 (#78), all in the MCP configuration area, plus the v1.1.29 bump.

1. Read <workdir>/.mcp.json — the Claude Code project file

Sources are now, lowest precedence first: <workdir>/.mcp.json → ~/.tact/.mcp.json
→ <workdir>/.tact/.mcp.json → installed plugins. A repository's shared configuration
works out of the box, but cannot silently take over a server the user declared — a
displaced declaration is still reported.

• It belongs to the project rather than the user, so an unparseable one is a warning and
  a skip, not the hard error a native config gets.
• McpProjectConfig gains enabled (default true) and a flattened extra map:
  • "enabled": false (the Codex convention) is resolved — it can shadow and be shadowed —
    but never connected; mcp list reports disabled (enabled: false), mcp get describes
    it without dialing.
  • Keys Tact does not model (enabled_tools, omit_tools_from, startup_timeout_sec,
    tools.<name>.output_token_limit) are named one by one in mcp list plus a warning in
    the log. The listing is the channel that matters: tact-ui installs a tracing subscriber
    only when RUST_LOG/tokio_console is set, so a warning alone would be invisible.

2. Fix plugin-bundle MCP parsing

A plugin-root .mcp.json using the standard {"mcpServers": {...}} wrapper was read as a
flat name→config map, producing a bogus server that was then skipped. parse_plugin_mcp_document
accepts the wrapper (which wins when present) and falls back to the flat form.

3. Rename the native MCP config to .mcp.json

Tact's two native config files were mcp.json (~/.tact/mcp.json, <workdir>/.tact/mcp.json)
while the same concept is .mcp.json everywhere else: Claude Code's project file, the file a
plugin bundle's mcpServers points at, VS Code's .vscode/mcp.json. Both scopes are now
.mcp.json, kept in the single MCP_CONFIG_FILE constant. Nothing is done for compatibility:
a leftover mcp.json is an unrelated file, neither a source nor reported.

Docs: Ch 8 source table and entry semantics, Ch 21, Ch 26 entry (en/zh), README.

Verification

• scripts/check-rust.sh green on the pushed tree: cargo fmt --check, clippy --all-targets -D warnings, and the four-crate test suite.
• no_proxy=127.0.0.1,localhost required for the loopback tests in this environment.