chore: release v0.3.0

Security hardening milestone:
- LLM prompts piped via stdin (no process table exposure)
- PID/log files in secure XDG_RUNTIME_DIR with atomic write
- Bounded LLM response reading (1MB stdout, 100KB JSON)
- Path traversal validation for diff paths and config
- 75 unit tests + 18 integration tests

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Alan Shum

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "semantic-diff"
-version = "0.2.3"
+version = "0.3.0"
 edition = "2021"
 description = "A terminal diff viewer with AI-powered semantic grouping (Claude CLI / Copilot)"
 license = "MIT"