fix(plugin): load the focused activation prompt

[admin-raintree]

Summary

• shorten the DocPull Codex activation prompt from 200 to 122 characters
• preserve the focused named-source trigger and cached-source/citation guidance
• add a regression test for Codex's 128-character host limit
• release the corrective package version as 6.5.3

Validation

• bun run validate:full (1,212 passed, 18 optional skips)
• plugin-creator validation
• focused activation-prompt and launcher regression tests