fix(factory): replace context spills with manifests

[walker-tx]

Eliminates model-managed Phase 1 spill consumption.

The context inspector now returns a ~1.5 KB validated manifest of approved paths and character counts instead of ~170 KB of raw contents requiring roughly 58 stateful reads. Downstream agents receive explicit phase-specific manifest paths and read only those files directly from /workspace.

Security properties retained and strengthened:

• canonical path and symlink rejection
• fixed allowlist and mandatory authority/persona/role/schema entries
• 40-file and 7,000-byte output bounds
• no raw context content in the manifest
• no repository discovery by child agents

Validation:

• full factory suite 13/13
• ShellCheck
• actionlint
• independent review: PASS