docs: add changelog for v0.1.0

changelog.md

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+# changelog
+
+## v0.1.0 (2025-12-29)
+
+initial release.
+
+### features
+
+- telegram bot bridge for openai codex cli using `codex exec` and `codex exec resume`
+- stateless session resume via `resume: <uuid>` lines embedded in messages
+- real-time progress updates with ~2s throttling, showing commands, tools, and elapsed time
+- full markdown rendering with telegram entity support (via markdown-it-py + sulguk)
+- concurrent message handling with per-session serialization to prevent race conditions
+- automatic telegram token redaction in logs
+- interactive onboarding guide for first-time setup
+- cli options: `--profile`, `--debug`, `--final-notify`, `--version`