refactor(cli): extract dispatch handlers

[cedric013]

Closes #1103
Closes #1107

Summary

• extract complex cli::dispatch::run branches into focused handler functions
• deduplicate setup repair handling shared by install/bootstrap
• replace internal runtime env mutation with centralized runtime flags while preserving env fallbacks
• keep CI-required OCLA import formatting and unused import cleanup

Validation

• cargo fmt --all -- --check
• cargo clippy --lib -- -D warnings
• cargo test cli::dispatch --lib

[yvgude]

Code Review: refactor(cli): extract dispatch handlers

Good architectural improvement — dispatch/mod.rs was overloaded and hard to navigate.

What it does:

• Extracts CLI command handlers from a monolithic match in dispatch/mod.rs into domain-specific handler functions
• Introduces core/runtime_flags.rs to replace direct env::set_var / env::var for LEAN_CTX_RAW, LEAN_CTX_COMPRESS, etc. (addresses #1107)
• 21 files touched, but net +333/-267 is modest — mostly moving existing code

Quality:

• Each handler becomes a self-contained function with clear responsibility
• runtime_flags eliminates unsafe set_var calls in multi-threaded context
• No logic changes in the extracted handlers — pure structural refactoring

Suggestion: Consider splitting runtime_flags into its own commit for a cleaner git history — it is orthogonal to the dispatch extraction.

Note: Import fixes overlap with main. Please rebase.

LGTM after rebase.

[yvgude]

Merged to main via CLI rebase+merge.