Support per-rule selection with --select and --ignore

[Johnkothapalli]

Problem

Teams may want to adopt a subset of rules or temporarily suppress a noisy rule without removing the analyzer from CI.

Proposed scope

Add repeatable or comma-separated --select and --ignore rule-ID options. Validate unknown IDs. Selection happens before analysis and must affect the cache profile so cached reports never leak findings from a different policy.

Acceptance criteria

• default behavior remains unchanged;
• unknown rule IDs produce a clear error;
• selection and ignore precedence is documented;
• cache keys include the effective rule set;
• tests cover select, ignore, precedence, invalid IDs, and cache isolation;
• README and changelog are updated.

This touches public CLI behavior; comment with proposed precedence before implementation.