Migrate to pi 0.99 (pi-ai + pi-agent-core together) #86

Dependabot bumped @earendil-works/pi-agent-core and @earendil-works/pi-ai to 0.99.2 separately (#84, #85), and both fail CI. Bumping the two together to ^0.99.2 still fails tsc -b, because 0.99 has breaking API changes:

• TranscriptContext no longer has systemPrompt / tools, and adds a brand field
• ToolCall.arguments is now JsonObject
• tool-result content types changed

The type errors are concentrated in the *-test-support, openclaw-port, opencode-port and pi-port code under packages/sdk and packages/memflywheel.

Scope:

• Upgrade pi-ai and pi-agent-core together to 0.99.x
• Adapt the ports and test support to the new types
• Group @earendil-works/* in .github/dependabot.yml so the two packages always move together

Replaces #84 and #85.