fix: spelling errors found by typos CLI

[luojiyin1987]

Spelling Errors Found

Running typos CLI found several spelling errors:

1. IDEALY → IDEALLY in docs/guide/installation.md:56
2. EXPLICITELY → EXPLICITLY in src/agents/orchestrator-sisyphus.ts:147
3. EXPLICITELY → EXPLICITLY in src/agents/sisyphus.ts:29

False Positives (ignored)

• preceeding - Intentionally matching misspelled API error messages in session recovery
• .edn - Valid Clojure file extension
• .typ - Valid Typst file extension

Changes

Fixed 3 genuine typos in documentation and agent prompts.