feat: add SVN (Subversion) working copy support

[xiaoye5200]

Summary

Adds first-class SVN support alongside the existing Git integration,
so that projects using Subversion can build and incrementally update
the knowledge graph without any manual configuration.

What changed

incremental.py

• find_svn_root() — walks up the directory tree to locate the SVN
  working-copy root (handles both SVN 1.6 per-directory .svn and
  the single-root layout introduced in SVN 1.7).
• detect_vcs(root) — returns "git", "svn", or "none" based on
  VCS markers at a given path. Used internally to dispatch to the
  correct VCS backend.
• find_repo_root() — now falls back to find_svn_root() when no
  .git directory is found.
• get_changed_files() — for SVN repos, uses svn status (working-
  copy changes) or svn diff --summarize -r rXXX:HEAD when the base
  parameter is a valid SVN revision range.
• get_staged_and_unstaged() — delegates to svn status for SVN repos.
• get_all_tracked_files() — tries svn list -R for SVN repos, falls
  back to a filesystem walk (which is also the existing Git fallback).
• _svn_revision_info() — reads branch path and revision number from
  svn info.
• _store_vcs_metadata() — helper that writes either
  git_branch/git_head_sha or svn_branch/svn_revision metadata
  depending on the detected VCS; used in both full_build() and
  incremental_update().
• Added .svn/** to DEFAULT_IGNORE_PATTERNS.

changes.py

• parse_svn_diff_ranges() — runs svn diff and feeds the unified-diff
  output into the existing _parse_unified_diff() for line-level change
  mapping. Accepts an optional revision range.
• parse_diff_ranges() — VCS-aware dispatcher: routes to the SVN or
  Git diff parser based on the presence of a .svn marker.
• analyze_changes() now calls parse_diff_ranges() instead of
  parse_git_diff_ranges(), so line-level risk scoring works for SVN
  diffs automatically.

tools/review.py — get_review_context uses parse_diff_ranges()
instead of parse_git_diff_ranges().

tools/__init__.py — exports parse_svn_diff_ranges and
parse_diff_ranges alongside the existing parse_git_diff_ranges for
backward compatibility.

cli.py — the status command shows SVN branch and revision number
for SVN working copies instead of the Git branch/SHA block.

Backward compatibility

All existing Git behavior is unchanged. The SVN path is only activated
when a .svn directory is detected; every function still accepts the
same parameters as before.

Testing

• Verified with a local SVN working copy (SVN 1.14, server-side).
• All existing test_incremental.py and test_changes.py tests pass
  without modification.
• Pre-existing Windows teardown failures (file-lock on SQLite temp
  files in teardown) are unrelated to this PR.

Notes

• svn list -R queries the server and may be slow on large repos;
  the filesystem-walk fallback kicks in automatically if it fails or
  times out.
• The base parameter semantics for SVN: a string matching
  r?\d+(:r?\d+|:HEAD|:BASE|:COMMITTED)? is treated as an SVN
  revision range; anything else (including the default "HEAD~1")
  is ignored and svn status is used instead.

[tirth8205]

This PR now has merge conflicts with main after recent merges to parser.py and related files. Could you rebase on the latest main?

[tirth8205]

In addition to the merge conflict, our review found this PR has zero tests for a 435-line feature addition. The _SAFE_SVN_REV regex is also duplicated across changes.py and incremental.py. Could you add tests and deduplicate the regex when you rebase?

[xiaoye5200]

Hi!
Since this PR was merged via squash merge, my GitHub account xiaoye5200 is not shown in the repository's contributor list, because the merged commit lost my original author attribution.

Could you please add the co-author trailer to the merged commit 40118f7:
Co-authored-by: xiaoye5200 948694243@qq.com

Once you update the commit message with this line, GitHub will automatically recognize my contribution and add me to the repository contributor list. Thank you very much!