Add 1.0.0 roadmap

[Korijn]

Adds ROADMAP.md: the PR-by-PR program to take patchdiff from 0.3.x to its first stable release, mirroring the series that took observ to 1.0.0 (observ #175–#197).

The program

14 PRs across 5 tracks:

• Track A — CI & benchmark infrastructure: modernize workflows (port of observ #182), replace the single-run 5% benchmark gate with observ's noise-robust interleaved guard at a 25% tripwire threshold (ports of observ #181 + #187).
• Track B — Documentation: MkDocs Material site with mkdocstrings API reference on GitHub Pages (port of observ #176), an Internals section (#179), a README rewrite (#180).
• Track C — Typing: runtime cleanups (#184) then full modern type hints with Operation TypedDicts, py.typed, and ty enforced in CI (#185), stacked.
• Track D — Test hardening: Hypothesis-based round-trip property tests plus the json-patch-tests RFC 6902 corpus (deliberate divergences skipped with reasons).
• Track E — Optimizations: two foundational passes (Myers O(ND) list diff to replace the O(m·n) DP; a produce() hot-path design pass) and three micro passes (diff/pointer, apply/iapply, proxy traps), each benchmark-verified against the new guard.
• Release: the 1.0.0 bump with release notes and before/after benchmark tables (#197).

Ordering is encoded in the roadmap: the benchmark guard lands before any optimization PR, and typing + property tests land before them as the safety net. 100% coverage stays enforced throughout.

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https://claude.ai/code/session_016Mu9vEBwU4fQLi8ZgkgdS2

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