fix: correct spelling errors (IDEALY→IDEALLY, EXPLICITELY→EXPLICITLY)

[luojiyin1987]

Fixes #936

Changes

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

Found via typos CLI spell checker.

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Summary by cubic

Corrects spelling in the installation guide and Sisyphus agent prompt text (“IDEALY”→“IDEALLY”, “EXPLICITELY”→“EXPLICITLY”) to improve clarity. No functional changes.

^{Written for commit d61817b. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.