docs: add v0.1.0rc1 prerelease notes

docs/release-notes-v0.1.0rc1.md

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+# TokenHelm v0.1.0rc1 — Release Candidate
+
+> ⚠️ **This is a release candidate, not a final release.** It is published to **TestPyPI only**
+> for final pre-publication validation. Do not use it in production. If validation passes, the
+> identical code ships as **v0.1.0** on public PyPI.
+
+## Purpose of this RC
+
+`v0.1.0rc1` is the last gate before the public release. It exists to verify, end-to-end, that:
+
+- the package **builds and publishes** through the automated OIDC pipeline (`release.yml`),
+- it **installs cleanly** from an index into a fresh virtual environment,
+- the **packaged data** (`pricing.yaml`, `py.typed`) and **all four adapters** are present,
+- the **examples run** against the installed package.
+
+No code changes are expected between `v0.1.0rc1` and `v0.1.0`.
+
+## Install (TestPyPI)
+
+TestPyPI does not host runtime dependencies, so add real PyPI as an extra index for PyYAML:
+
+```bash
+python -m venv .venv && . .venv/bin/activate        # Windows: .venv\Scripts\activate
+
+pip install --index-url https://test.pypi.org/simple/ \
+            --extra-index-url https://pypi.org/simple/ \
+            "tokenhelm==0.1.0rc1"
+
+# with all provider extras
+pip install --index-url https://test.pypi.org/simple/ \
+            --extra-index-url https://pypi.org/simple/ \
+            "tokenhelm[all]==0.1.0rc1"
+```
+
+## Validation checklist
+
+```bash
+python -c "import tokenhelm; print(tokenhelm.__version__)"          # -> 0.1.0rc1
+python -c "import importlib.resources as r; \
+           assert (r.files('tokenhelm')/'data'/'pricing.yaml').is_file(); \
+           assert (r.files('tokenhelm')/'py.typed').is_file(); print('data + py.typed OK')"
+python -c "from tokenhelm.adapters import default_adapters; \
+           print([a.provider.value for a in default_adapters()])"   # openai, anthropic, gemini, ollama
+python examples/openai_quickstart.py
+python examples/anthropic_quickstart.py
+python examples/custom_logger.py
+```
+
+Expected: imports succeed, data files packaged, four adapters load, examples print a normalized
+event. (All of this is already verified locally against the built wheel.)
+
+## What's in this release
+
+The full feature set and detailed notes are in
+**[release-notes-v0.1.0.md](release-notes-v0.1.0.md)**. In brief:
+
+- Core SDK: `track()`, `trace()` (sync **and** async), `track_stream()` (sync/async, wrap or
+  manual), `configure()`.
+- Immutable, normalized `LLMEvent` (eight mandated fields + `usage_complete`/`priced` flags).
+- Four provider adapters — **OpenAI, Anthropic, Gemini, Ollama** — non-streaming and streaming.
+- Five extension points: `BaseAdapter`, `PricingProvider`, `EventDispatcher`, `Logger`,
+  `StorageBackend`.
+- 127 tests, 95.62% coverage; `track()` ≈ 0.011 ms, streaming adds ≈ 0 MiB.
+
+## Known limitations
+
+See the *Known limitations* section of
+[release-notes-v0.1.0.md](release-notes-v0.1.0.md#known-limitations): duck-typed provider
+identification, streaming validated against captured fixtures, static bundled pricing, and
+sync-only `track()`.
+
+## Feedback
+
+Found a problem with the RC? Please open an issue
+(https://github.com/srinitrumatics/tokenhelm/issues) or start a discussion
+(https://github.com/srinitrumatics/tokenhelm/discussions) and mention `v0.1.0rc1`.
+
+## After validation
+
+If the checklist above passes from TestPyPI, we cut **v0.1.0** and publish to public PyPI via
+the same OIDC pipeline. See [go-live-checklist.md](go-live-checklist.md) for the full procedure.