feat(installer): implement Phase 3 — the patch tier

Two features need edits to stock ServUO sources, because the events they
depend on do not exist. This adds the rung ladder of PLAN.md §2.2.1, the
unsupported-version path of §2.2.2, and the record and cache Phase 4 will read.

Three decisions were not settled by the plan:

* The engine is fully native, with no `git`. §2.2.1 wrote rung 1 as "apply
  verbatim with git apply", but §1 chose the release tarball specifically so
  there would be no git on the shard host, and rung 2 needs a native applier
  regardless. Rung 1 keeps its distinct, stronger verdict — the whole file
  reproduced the diff's `index` pre-image, computed as a git blob SHA1 in
  process — while the write goes through the same code path as rung 2. On the
  real trees here that is not academic: the shipped .patch files are CRLF in a
  Windows checkout and two of their three targets are LF, so `git apply`
  refuses patches this applies correctly.

* Per-patch metadata is declared by the release, with a built-in fallback.
  Which patches form one all-or-nothing unit, which companion .cs follows
  which, whether a CORE rebuild is needed and what declining costs are not
  derivable from a diff. servuo-plugins now declares them; overlay v0.1.1 is in
  the current bundle and declares nothing, so a built-in copy stands in for it.
  A checked-in fixture of the release workflow's own jq output asserts the two
  descriptions are identical, so the repos cannot drift quietly.

* Pre-images are cached in the state directory. The tier edits files the
  operator owns, and `/etc/runicgateway/patches/originals/` is what turns "here
  are the hunks we added" into a revert anyone can verify — kept out of the
  ServUO tree, which uninstall has promised never to clean up.

Everything else follows §2.2.1: exact matching with only line-ending and
trailing-whitespace normalization, exactly one occurrence or it fails,
all-or-nothing per patch file and again per feature, and a byte-preserving
splice so nothing outside a hunk can be reformatted.

Verified against the ServUO 57.4 tree on this machine across four scratch
roots: a hand-patched tree (rung 0), a reverse-applied stock one (rung 1 on the
real EventSink.cs, its blob matching the patch's declared pre-image), a
mixed-rung feature, a tree with edits inside two patched regions (rung 3 —
nothing written, nothing held back applied, no companions copied), and a
non-57.4 tree both with and without the extra consent flag. Three consecutive
runs left install.json byte-identical and the cached pre-image still pre-patch.

Three reporting defects the live runs caught are fixed with tests: a dry run
and a held-back patch both claimed to be "applied", the core-rebuild warning
fired when nothing had been written and named a Scripts file as core, and a
declined tier announced the loss of features install.json showed as applied.
Refused patches are now cached too, since the refusal message names that path.

Refs: docs/installer/PLAN.md §2.2, §5 Phase 3

Co-Authored-By: Claude <noreply@anthropic.com>

src/cli.rs

@@ -2,20 +2,20 @@
 //!
 //! The shape here is not invented: `docs/installer/INSTALL.md` §2 was written before the binary and
 //! fixes every command and flag an operator can type. This module parses that surface *whole*, even
-//! though Phase 1 implements only part of it — a parser written once against the published contract
-//! cannot drift from it, and a flag that belongs to a later phase gets an explicit "not in this
-//! build" notice at the point where it would have taken effect (see `install.rs`). The one thing it
-//! must never do is accept `--patches` silently, which would let an operator believe stock ServUO
-//! files were touched when nothing was.
+//! where a later phase implements it — a parser written once against the published contract cannot
+//! drift from it, and a flag belonging to an unbuilt phase gets an explicit notice at the point
+//! where it would have taken effect (see `install.rs`). The tri-state on `--patches` is the part
+//! that carries weight: "not mentioned" has to stay distinguishable from "explicitly declined",
+//! because only the first may prompt and only an explicit yes may edit a stock ServUO file.
 //!
 //! Hand-rolled, like `link/sidecar/src/cli.rs`: a handful of flags, no completions, no subcommand
 //! trees. A parsing crate would be larger than the code it replaced.
 
 use std::fmt;
 
-/// The verb. `Install` is the only one Phase 1 implements; the rest parse so that running them
-/// reports which phase they arrive in rather than "unrecognized argument", which would read as a
-/// typo rather than as an unfinished tool.
+/// The verb. `Install` is the only one built so far; the rest parse so that running them reports
+/// which phase they arrive in rather than "unrecognized argument", which would read as a typo
+/// rather than as an unfinished tool.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Command {
     Install,