chore: release v0.3.0

[mgoldsborough]

Cuts the first synapse-research release that can anchor research on a workspace file via the `ai.nimblebrain/host-resources` extension (Phase 2c).

What ships in v0.3.0

• New: `seed_uri` parameter on `start_research` — agent passes a `files://` URI; the server reads it via the host-resources extension. Preferred path on hosts that advertise the capability — keeps the agent's context budget free of file bytes.
• New: `seed_data` parameter on `start_research` — agent passes raw text inline. Universal fallback that works on every host. Required for hosts without the extension.
• Mutually exclusive: passing both is rejected as ambiguous.
• Capability- or scheme-missing errors carry the Level-C retry hint ("pass `seed_data` inline") so agents have an actionable recovery path.
• Seeds above 400 KB are truncated with a visible marker; empty text resources surface a distinct error from binary; the `research_run` entity records `seed_content_chars`.
• Drive-by: manifest `briefing.priority` corrected from `"normal"` to `"medium"` (was never valid against the platform's host schema enum; blocked install on current platform main).

Closes the original production bug where the agent couldn't anchor a research run on an uploaded workspace file.

Dependency change

• Adds `nimblebrain-bundle-sdk>=0.1.0` (now on PyPI).

Test plan

• `uv run pytest tests/` green — 54 passing (43 existing + 11 in `test_seed_uri.py`).
• Validated end-to-end on a local platform: uploaded a 2,558-byte CSV, called `start_research` with `seed_uri`, confirmed seed content reached the gpt-researcher prompt and `seed_content_chars: 2554` landed on the entity.
• After merge: create GitHub Release `v0.3.0`. The `Release MCPB Bundle` workflow auto-builds linux-amd64, linux-arm64, darwin-arm64 `.mcpb` bundles and attaches them to the release.
• Confirm bundles publish to mpak.

Known follow-ups (not blockers)

• `synapse-research#9` — `start_research` dispatched inline rather than task-augmented; bundle's worker finishes but the agent surfaces a 3-minute timeout. Pre-existing, surfaced during local validation.
• `upjack#30` — log spam on every `validate_entity` call. Pre-existing.