feat(mcp): investigation-grade trace output + impact analysis + process steps

Major rewrite of trace_call_path output for investigation-grade quality:

Categorized edges (Fixes A+D):
- incoming: { calls: [...], imports: [...], extends: [...] }
- outgoing: { calls: [...], has_method: [...], extends: [...] }
- Separate transitive_callers for depth > 1 (avoids noise in main results)
Each category queried independently via single-hop BFS on specific edge types.

Broader caller coverage (Fix A):
- Include USAGE and RAISES edges alongside CALLS for incoming queries
- Query both the Class node and its methods as BFS roots
- Result: MeteorError upstream goes from 9 to 39 callers

Noise elimination (Fix C):
- Default depth 1 for categorized results (direct only)
- Transitive callers isolated in separate field, capped at 50
- No more 106 render() methods polluting results

New get_impact tool (Fix F):
- BFS upstream/downstream with depth-grouped results
- d1_will_break / d2_likely_affected / d3_may_need_testing
- Risk assessment: LOW / MEDIUM / HIGH / CRITICAL based on d1 count
- Affected processes cross-referenced by name
- Tested: protectedUpdate returns CRITICAL (38 direct, 162 transitive)

New get_process_steps tool (Fix E):
- Returns ordered step list for a specific process ID
- Each step includes name, qualified_name, file_path
- Enables step-by-step flow debugging

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