feat(project): Project.llmProvider semantically names an Llm resource

Why: Phases 0-3 built the server-managed Llm registry; this phase pivots the
existing Project.llmProvider column from "local provider hint" to "named Llm
reference" so operators can pick a centralised Llm per project. No schema
change — the column stays a free-form string for backward compat.

- `mcpctl create project --llm <name>` (+ `--llm-model <override>`) sets
  llmProvider/llmModel to a centralised Llm reference, or 'none' to disable.
- `mcpctl describe project` fetches the Llm catalogue alongside prompts and
  flags values that don't resolve with a visible warning. 'none' is treated
  as an explicit disable, not an orphan.
- `apply -f` doc comments updated; --llm-provider still accepted but now
  documented as naming an Llm resource.
- New `resolveProjectLlmReference(mcpdClient, name)` helper in mcplocal's
  discovery: returns `registered`/`disabled`/`unregistered`/`unreachable`.
  The HTTP-mode proxy-model pipeline will consume this when it pivots to
  mcpd's /api/v1/llms/:name/infer proxy.
- project-mcp-endpoint.ts cache-namespace path gets a comment explaining
  the new resolution order — behavior unchanged, just clarified.

Tests: 6 resolver unit tests + 3 new describe-warning cases. Full suite
1853/1853 (+9 from Phase 3's 1844). TypeScript clean; completions
regenerated for the new create-project flags.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

completions/mcpctl.fish

@@ -344,6 +344,8 @@ complete -c mcpctl -n "__mcpctl_subcmd_active create secretbackend" -l force -d
 complete -c mcpctl -n "__mcpctl_subcmd_active create project" -s d -l description -d 'Project description' -x
 complete -c mcpctl -n "__mcpctl_subcmd_active create project" -l proxy-model -d 'Plugin name (default, content-pipeline, gate, none)' -x
 complete -c mcpctl -n "__mcpctl_subcmd_active create project" -l prompt -d 'Project-level prompt / instructions for the LLM' -x
+complete -c mcpctl -n "__mcpctl_subcmd_active create project" -l llm -d 'Name of an Llm resource (see \'mcpctl get llms\'), or \'none\' to disable' -x
+complete -c mcpctl -n "__mcpctl_subcmd_active create project" -l llm-model -d 'Override the model string for this project (defaults to the Llm\'s own model)' -x
 complete -c mcpctl -n "__mcpctl_subcmd_active create project" -l gated -d '[deprecated: use --proxy-model default]'
 complete -c mcpctl -n "__mcpctl_subcmd_active create project" -l no-gated -d '[deprecated: use --proxy-model content-pipeline]'
 complete -c mcpctl -n "__mcpctl_subcmd_active create project" -l server -d 'Server name (repeat for multiple)' -x