Improve payload construction, size enforcement, and full scan correctness

[Rishabh4275]

Motivation and Context

Several issues were identified during live testing of the Purview GitHub Action:

1. Full scan included PR files — getAllRepoFiles() used filesystem glob which reads from the PR HEAD checkout, incorrectly including files added in the PR when the full scan
   should only cover the base/pre-PR state.
2. No payload size enforcement for commits — commit-level PCA, inline PC, and upload signal requests had no size validation, causing 413 errors on large commits.
3. PCA batch item count exceeded API limit — the API enforces a max of 64 items per processContentAsync batch, but the batching logic only checked byte size, causing
   ProcessContentBatch request has item count greater than 64 errors.
4. Noisy logging — ~30 log statements inside nested loops (per-file, per-user, per-commit) flooded the output, making it hard to follow the actual flow.
5. file-patterns: '' excluded subdirectories — minimatch('src/index.ts', '') returns false because * doesn't cross / boundaries, so patterns like * and *.ts silently
   excluded all nested files.
6. accessedResources lacked structured identifiers and the isCrossPromptInjectionDetected field required by the API.
7. dist/ tracked unnecessary build artifacts — the full tsc output (.d.ts, .js.map, subdirectories) was committed when only the ncc-bundled dist/index.js is needed at
   runtime.

Description

Full scan correctness

• getAllRepoFiles(atRef?) now accepts an optional git ref. When provided (PR base SHA or push before SHA), it uses git ls-tree + git cat-file instead of filesystem glob,
  ensuring only files from the pre-event state are scanned.
• Added git fetch --depth=1 origin to handle shallow clones where the base SHA isn't available locally.

Payload size enforcement (two-tier system)

• maxContentSize (3 MB) — content data field limit; triggers chunking into multiple parts with Part: N in accessedResources names.
• maxRequestSize (3.7 MB) — total request limit; triggers batch/request splitting. AccessedResources are included in the size calculation.
• maxBatchItems (64) — API item count limit per PCA batch; enforced alongside byte size in both file and commit batch-splitting loops.
• Added splitCommitRequests() helper that handles content splitting first, then accessedResources splitting for extreme cases (e.g., commits with 500+ files).
• buildCommitProcessContentRequest now returns ProcessContentRequest[] (was singular) and buildCommitUploadSignalRequest now returns UploadSignalRequest[] (was singular),
  with all callers updated.

accessedResources improvements

• Identifier format: PR: Commit: when PR is available; Commit: otherwise (full scans, push events).
• File name format: Repo: File: Path: .
• Commit name format: Repo: Commit: .
• isCrossPromptInjectionDetected: false set on all accessed resources.
• Part: N suffix appended to names only when content/resources are split.