refactor: no feature depends on Gemini any more

Depleted Gemini prepayment credits took out PDF rendering. The same key was the
only thing standing between level-up proposals and the same fate, so both are
off it.

- `pdf_renderer` is DELETED, not disabled. Nothing sets `render_pdf: true` since
  markdown became the deliverable (821cbb8), so the worker polled forever for
  rows that can no longer exist. It was also the only caller of the Gemini
  MD->HTML conversion. A worker that cannot do anything is worse than absent: it
  reads as a feature.

- `level_up` now resolves its proposer through the provider REGISTRY
  (`Runtime::resolve_provider`), the same path the evaluator uses, defaulting to
  `glm:glm-4.7` — the validator this project measured and chose in
  scripts/judge-eval.sh. `CLAWMATES_LEVEL_UP_MODEL` takes a registry spec
  (`glm:glm-4.7`, `kimi:k2`, `claude-sonnet-5`), so every provider the platform
  can already reach works and no single vendor's billing can take it down.

The non-obvious part of that swap: Gemini was asked for
`response_mime_type: application/json` and obliged, so the old code parsed the
raw reply. Anthropic-format models are under no such obligation and wrap objects
in prose or a ```json fence. `extract_json_object` brace-counts to the matching
close — string-aware, so a `}` inside a value does not end it, and nested (these
proposals nest by design). Tested against bare, fenced, nested, brace-in-string
and absent. Parsing raw text would have worked in review and failed on the first
real proposal.

What deliberately still MENTIONS Gemini: `mission_runtime` forwards
GEMINI_API_KEY to agent containers alongside GROQ/OPENAI/ZAI/KIMI, and the claw
model selector offers it. Those are user options, not platform requirements —
the ask was to remove the NEED.

Also corrected a comment in mission_delivery that cited `pdf_renderer` as the
authority on artifact path resolution. It never was: it joined the mission id
first and produced a doubled path that never resolved.

238 lib tests, 20 test binaries.

crates/cm-api/src/mission_delivery.rs

@@ -443,8 +443,11 @@ pub async fn capture_phase_diff_at(
     )
     .map_err(|e| format!("write delivery.json: {e}"))?;
 
-    // Path is stored relative to the missions root, matching how
-    // `pdf_renderer` resolves artifact paths.
+    // Path is stored relative to the MISSIONS ROOT — the convention every
+    // artifact uses, and what `routes::missions::artifact_content` resolves
+    // against. (The old `pdf_renderer` claimed to match this and did not: it
+    // joined the mission id first, producing a doubled id and ENOENT. It is
+    // gone; this comment named it as the authority, which it never was.)
     let rel = format!("_outputs/{mission_id}/{phase_id}/diff.patch");
     cm_db::repo::missions::register_artifact(
         pool,