docs: add Talos-specific AGENTS.md and tighten CONTRIBUTING.md; add beta assessment docs

[ai21z]

Motivation

• Provide a concrete, evidence-first audit/playbook for Talos as a local-first execution harness because the prior AGENTS guidance was generic and insufficient for release-quality audits.
• Codify non-negotiable invariants (secrets, approval gates, workspace sandboxing, trace evidence) so audits produce deterministic tests and actionable fixes.
• Align contributor guidance with the repo’s local-first, no-network-by-default policy and the near-term extractor/UX phase plan.

Description

• Added AGENTS.md (Talos CLI Audit & Development Guardrails) which specifies execution doctrine, required live-audit artifacts, a mandatory finding schema, severity policy, and P0 invariants that block release.
• Rewrote and condensed CONTRIBUTING.md into a LOQ-J–specific contributor guide that documents build/test flows, local-first security rules, indexing/RAG guarantees, CLI UX rules (TTY/spinner/ASCII fallback), PR/DoD expectations, and near-term roadmap items.
• Added archived and readable assessment artifacts (docs/archive/v0.9.0-beta_assessment_version1.md and docs/v0.9.0-beta_assessment.md) capturing the v0.9.0-beta evaluation and proposed phase/PR plan.
• Small repo housekeeping: committed the new/updated docs files and updated repository guidance; these are documentation-only changes and do not modify runtime code.

Testing

• Performed repository verification commands: inspected AGENTS.md and CONTRIBUTING.md, staged and committed the changes with git add/git commit.
• No unit or integration tests were run as part of this PR because the changes are documentation-only; please run ./gradlew test and the REPL smoke checks (:reindex --full, :files, two-file compare, Auto→Ask trivia) in CI or locally before merging.
• Recommended CI: require ./gradlew test green and a quick smoke transcript (copy/paste) validating :reindex and :files behaviors as part of PR gating.

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Codex Task