fix: accept raw-string (r""") docstring openers in both parsers

[Jammy2211]

Closes #250.

Two independent PyAutoHands docstring parsers silently mis-handled an r""" opener. Neither raised, and there are currently zero raw narrative docstrings in any workspace, which is why this never fired.

This blocks the 41-file workspace raw-stringing task (PyAutoMind draft/maintenance/workspaces/latex_raw_string_docstrings.md): those tutorial docstrings carry LaTeX and must be raw — unprefixed, \theta is a TAB followed by heta — and raw is exactly what these two parsers rejected.

The two defects

add_notebook_quotes._narrative_docstring_ranges tested lines[start].startswith('"""'). A raw block is a perfectly good column-0 ast.Expr(Constant(str)), so it reached that test and failed it — the block was dropped as a cell boundary and the tutorial prose shipped as a Python code cell containing a bare string literal.

env_config._DOCSTRING_DELIM_RE matched a bare delimiter only. An r""" opener was walked past and the block's closer matched as an opener instead, inverting docstring parity for the rest of the file: an __Env__ section further down was read as if it sat outside a docstring and read_env_declaration returned None, silently losing the ENV: declaration and rerouting the script's smoke profile. Seven autolens_workspace scripts carry __Env__ sections.

Reproduced against main @ cdea28c on a probe pair differing only by an r:

	before	after
_narrative_docstring_ranges	[(6,10)] — raw block dropped	[(0,2), (6,10)]
read_env_declaration	None	['jax']

The change

Both sites accept an optional r/R prefix on either delimiter. The notebook converter replaces the opener line outright when it emits the cell, so the prefix never reaches the generated artefact and output is byte-identical — which is what makes the downstream task's diff-empty gate meaningful.

Six regression tests, each verified to fail with the source change reverted:

• test_add_notebook_quotes — raw block converts byte-identically to the same block unprefixed; all six prefix/delimiter forms produce identical output.
• test_env_config — the parity case (declaration survives an earlier raw docstring, which a single-block test would miss); declaration inside the raw block itself; all six forms parse.
• test_strip_env_declarations — an __Env__ section in a raw block strips as a plain one does.

Verification

• Full suite 14 failed / 337 passed on this branch vs 14 failed / 331 passed on main — identical failure sets. All 14 are ipynb-py-convert failing to build in the dev container; CI installs it, so they run green here.
• Boundary set confirmed not to have widened: column-0 raw single-quoted strings, assigned literals, raw bytes literals and f-strings all remain non-boundaries.
• generate_markdown.script_title verified unaffected (its regex finds the """ after the r, same title either way); navigator reads already-converted output.

Notes for the reviewer

• The notebook-level assertion the issue sketched is made on the converted source instead: the converter replaces the opener line outright, so byte-identical conversion is the tighter claim, and it does not depend on ipynb-py-convert.
• No reformatting: this repo is not black-formatted (44 files on main would change), so the new code matches surrounding style rather than a formatter.
• Independent of feature/hands-hygiene-leftovers — that branch touches AGENTS.md, generate_release_notes.py, bin/autohands and two unrelated tests, so there is zero file overlap and the two can merge in either order.

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https://claude.ai/code/session_01MTjtx5mdituitiyQYFGn2E

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