refactor(llm-deepseek)!: rename the provider route to deepseek-official

The native adapter's route was named deepseek, colliding with pi-ai's
catalog provider of the same name, so the two DeepSeek paths could never
be mounted side by side. The web settings page needs both configurable at
once. Compositions, fixtures, goldens, scaffolding defaults, and docs all
move together (pre-release, no shim); TUI/session-query-spill/
missing-credential goldens re-recorded through their keyless refresh
modes because provider-name length shifts box padding and spill
truncation points.

examples/headless-agent/tests/full-loop.e2e.ts

@@ -29,7 +29,7 @@ describe.skipIf(!process.env.DEEPSEEK_API_KEY)('full loop: real model + real bas
   it('runs a bash command on request and reports its output', async () => {
     workdir = await mkdtemp(join(tmpdir(), 'dsh-full-loop-e2e-'))
     ctx = await codingHarness(workdir, { persona: SYSTEM_PROMPT })
-    const agent = ctx.agentLoop.create(SessionId('e2e-loop'), { provider: 'deepseek', model: 'deepseek-v4-flash' })
+    const agent = ctx.agentLoop.create(SessionId('e2e-loop'), { provider: 'deepseek-official', model: 'deepseek-v4-flash' })
 
     agent.followup(createUserMessage({ content: [{ type: 'text', text: 'Run `echo e2e-ok` with the bash tool and tell me its exact output.' }], source: { kind: 'user' } }))
     await waitForIdle(ctx, agent)