v0.10.1 - Clearbox-only Reddit source contract

The Reddit engine now has one explicit opportunity source: Clearbox. This patch removes the legacy parallel discovery path so the public architecture, runnable starter, and reusable agency skill all teach the same source contract.

Changed

• Clearbox-only source contract: pull.py imports a complete Clearbox export and requires the stable opportunity id, original lead/engage/competitor disposition, and exact Reddit permalink.
• Safe offline path: the bundled synthetic Clearbox export exercises the same contract without copying over a user's live export.
• Aligned public guidance: the engine guide, agency skill, AI-visibility playbook, proposal skill, examples, and GTM starter language now describe Clearbox as the authoritative opportunity source.
• Profile evidence terminology: the optional Playwright tier is described as a rendered-profile check, not as a Reddit collection path.

Removed

• Legacy discovery client and configuration: removed the external Reddit discovery client, its environment-key path, and the keyword/subreddit source files.

Verification

• Added importer tests for complete-export handling, truncation refusal, source-field validation, and exact permalink preservation.
• Added a release scan rule that rejects the retired source path from active Reddit engine surfaces.