test: add full core-components coverage plan

[kvinwang]

Summary

• add a source-derived full test plan for Guest OS, VMM, KMS, Gateway, Verifier, and cross-component integration
• inventory every relevant source file, RPC method/message/field, example configuration field, and source-only configuration field with reverse test-case traceability
• cover functional, regression, security, lifecycle, simulator-versus-hardware, and pinned mixed-version compatibility behavior
• add the PR docs: add KMS upgrade plan for operators #705 KMS onboard matrix, including the 0.5.4 bridge, 0.5.8/0.5.11 direct paths, legacy TDX constraint, RA-TLS OID rejection, ACPI age matching, identity continuity, rollback, and post-KMS gateway cutover

Scale

• 6 chapters
• 55 sections
• 361 test cases
• 106 RPC methods
• 147 protobuf message schemas / 502 fields
• 214 example configuration leaves plus 43 source-only configuration field names
• 653 inventoried source files, all mapped to valid test cases

Validation

• python3 -m unittest discover -s tools/dstack-test/tests -v
• prek run --all-files
• reuse lint
• git diff --check
• plan loader/render validation
• duplicate ID, anchor, link, API/config reference, and source-map consistency audit (0 errors)

Dependency

Stacked on #823 (docs/test-methodology-tool) because this plan uses the test-plan format and runner introduced there.

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