Fix agent send attribution auth

[KyleAMathews]

Summary

• include both from_principal/from_agent plus the active wake write token on runtime-originated sends
• allow server send attribution when from_agent is backed by a valid active agent write token
• keep spoofed from_agent rejection and add coverage for the write-token path

Tests

• pnpm --filter @electric-ax/agents-mcp build
• pnpm --filter @electric-sql/client build
• pnpm --filter @electric-ax/agents-runtime build
• cd packages/agents-server && pnpm vitest run test/electric-agents-routes.test.ts -t "send endpoint"
• cd packages/agents-runtime && pnpm vitest run test/process-wake.test.ts -t "executes send via server API"
• pnpm --filter @electric-ax/agents-runtime typecheck
• pnpm --filter @electric-ax/agents-server typecheck

[github-actions]

Electric Agents Desktop Builds

Build artifacts for commit 65e79e3.

Platform	Status	Artifact
macOS Apple Silicon	Passed	DMG
macOS Intel	Passed	DMG
Windows x64	Passed	Installer
Linux x64	Passed	AppImage / deb

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.98%. Comparing base (cb6ae57) to head (65e79e3).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4522      +/-   ##
==========================================
+ Coverage   54.88%   54.98%   +0.09%     
==========================================
  Files         307      307              
  Lines       34522    34545      +23     
  Branches     9871     9876       +5     
==========================================
+ Hits        18949    18993      +44     
+ Misses      15554    15533      -21     
  Partials       19       19              

Flag	Coverage Δ
packages/agents	71.89% <ø> (ø)
packages/agents-mobile	84.09% <ø> (ø)
packages/agents-runtime	80.99% <100.00%> (+0.01%)	⬆️
packages/agents-server	73.11% <100.00%> (+0.34%)	⬆️
packages/agents-server-ui	5.89% <ø> (ø)
packages/electric-ax	46.42% <ø> (ø)
typescript	54.98% <100.00%> (+0.09%)	⬆️
unit-tests	54.98% <100.00%> (+0.09%)	⬆️

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[github-actions]

Electric Agents Mobile Build

Local mobile checks ran for commit 65e79e3.

The EAS Android preview build was skipped because the mobile-eas-build label is not present.
Add the mobile-eas-build label to this PR to produce an installable preview build.

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