feat(opencode): add PowerContext integration

[happy-v587]

Which issue or RFC does this PR close?

Closes #1330.

Tracking issue: #1213.

Rationale for this change

PowerContext supports several coding-agent hosts but did not have a native OpenCode integration. This adds project-scoped recall, prompt capture, and curated durable-context tools while keeping the PowerContext Server as the single runtime and storage boundary.

What changes are included in this PR?

• Add a native OpenCode 1.x plugin with bounded automatic recall, independent prompt capture, fail-open HTTP behavior, Git-based scope mapping, secret filtering, and curated pc_* tools.
• Require confirmation for durable tool mutations while keeping Candidate approval and rejection as explicit human operations.
• Add powercontext setup opencode and powercontext doctor opencode, including OpenCode version validation and an ownership-protected global project-context Skill installation.
• Generate the OpenCode operation table from openapi/powercontext.yaml and add TypeScript, CLI, contract, packaging, and isolated real-OpenCode validation.
• Add English and Chinese setup documentation and navigation entries.

Are there any user-facing changes?

Yes. Users can install the integration with:

powercontext setup opencode --source oceanbase/powercontext --ref master

The plugin requires OpenCode 1.18.21 or newer in the 1.x line. Configuration uses the POWERCONTEXT_OPENCODE_ environment prefix. This change does not modify the HTTP API, persisted formats, or existing integration behavior.

How was this change tested?

• make check
• make test — 644 passed, 13 skipped
• make contract-test — 29 passed
• make opencode-test — 10 Vitest tests, TypeScript check, and bundle build
• make docs-test
• make build
• Isolated real OpenCode 1.18.21 installation with powercontext setup opencode followed by a successful three-check powercontext doctor opencode

AI usage statement

OpenAI Codex (GPT-5) was used to inspect the repository and OpenCode plugin contract, implement the integration, write tests and documentation, resolve the latest-base conflicts, and run verification.

[happy-v587]

@PsiACE PTAL

[Teingi]

LGTM