feat(skills): add hindsight-memory skill for persistent agent memory

[benfrank241]

Summary

• Adds a new hindsight-memory agent skill that teaches sandboxed agents how to use Hindsight for persistent memory across ephemeral sandbox sessions
• Includes 5 workflows: recall before work, retain after work, reflect for synthesis, retain-files for bulk import, and cross-sandbox continuity via session bookends
• Ships with a CLI reference, example network policy (read-write to Hindsight API), and covers both cloud and self-hosted deployments
• Updates CONTRIBUTING.md skills table with the new entry under Platform

Closes #371

Changes

File	What
.agents/skills/hindsight-memory/SKILL.md	Skill definition with setup, 5 workflows, policy examples, companion skills table
.agents/skills/hindsight-memory/cli-reference.md	Hindsight CLI command reference with flags and API endpoints
.agents/skills/hindsight-memory/example-policy.yaml	Complete sandbox policy template for Hindsight API access
CONTRIBUTING.md	Added hindsight-memory to the skills inventory table

Test plan

• Skill files are valid markdown with correct YAML frontmatter
• example-policy.yaml validates against the policy schema in architecture/security-policy.md
• Skill is discoverable by agent harnesses via .agents/skills/ directory convention
• CLI commands in the skill and reference match the current Hindsight CLI

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[benfrank241]

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[benfrank241]

recheck

[johntmyers]

This does not conform to our contributing requirements and is the PR is functionally un-sound.

[benfrank241]

Thanks for the review @johntmyers. Could you share specific details on what doesn't conform or what's functionally unsound? Happy to fix — just want to make sure I address the right things.

A few areas I'm already aware could use improvement:

• The --config HINDSIGHT_API_URL in the provider create example uses a bare key without =VALUE, which may not be valid for --config (it is for --credential)
• The PR body used a custom format rather than the PR template sections

If there are other issues (policy format, command syntax, style), I'd appreciate knowing so I can get them all in one pass.