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/resume.e2e.ts

@@ -40,7 +40,7 @@ describe.skipIf(!process.env.DEEPSEEK_API_KEY)('resume: continue a persisted ses
     ctx = await codingHarness(process.cwd(), { persona: SYSTEM_PROMPT, persistenceRoot: root })
     const first = (await ctx.agents.create({
       sessionId: SESSION_ID,
-      agentOptions: { provider: 'deepseek', model: 'deepseek-v4-flash' },
+      agentOptions: { provider: 'deepseek-official', model: 'deepseek-v4-flash' },
     })).agent
     first.followup(createUserMessage({ content: [{ type: 'text', text: `Remember this code for later: ${SECRET}. Just acknowledge it.` }], source: { kind: 'user' } }))
     await waitForIdle(ctx, first)
@@ -53,7 +53,7 @@ describe.skipIf(!process.env.DEEPSEEK_API_KEY)('resume: continue a persisted ses
     ctx = await codingHarness(process.cwd(), { persona: SYSTEM_PROMPT, persistenceRoot: root })
     const resumed = (await ctx.agents.resume({
       resumeSessionId: SESSION_ID,
-      agentOptions: { provider: 'deepseek', model: 'deepseek-v4-flash' },
+      agentOptions: { provider: 'deepseek-official', model: 'deepseek-v4-flash' },
     })).agent
     expect(resumed.session.id).toBe(SESSION_ID)
     // The prior user turn is in the rehydrated log before the model is asked.