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/record.rs

@@ -43,7 +43,13 @@ pub struct InstallRecord {
     /// in the other direction. Read it with [`InstallRecord::link_record`].
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub link: Option<serde_json::Value>,
-    /// Phase 3 (applied patches, with the rung that applied each). Carried through untouched.
+    /// The patch tier: one entry per feature actually in place, with the rung that applied each of
+    /// its patches (Phase 3).
+    ///
+    /// Raw JSON for the same reason as [`InstallRecord::link`] — a record written by a newer
+    /// installer survives a re-run here intact. Read it with [`InstallRecord::patch_records`].
+    /// Only features that are *applied* appear: a declined or refused one left no trace in the
+    /// tree, and recording it would make `doctor` and `uninstall` report work nobody did.
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub patches: Vec<serde_json::Value>,
     /// Anything a newer installer wrote that this one has no name for.
@@ -203,6 +209,19 @@ impl InstallRecord {
     pub fn link_record(&self) -> Option<LinkRecord> {
         serde_json::from_value(self.link.clone()?).ok()
     }
+
+    /// The patch-tier entries this build understands.
+    ///
+    /// An entry it cannot parse is dropped from the returned list but still carried through on
+    /// save, exactly as with [`Self::link_record`]. The consequence of a dropped entry is that this
+    /// run re-derives that feature's state from the tree — which the rung ladder answers correctly
+    /// on its own — rather than an older installer refusing to run on a newer host.
+    pub fn patch_records(&self) -> Vec<crate::patch::FeatureRecord> {
+        self.patches
+            .iter()
+            .filter_map(|v| serde_json::from_value(v.clone()).ok())
+            .collect()
+    }
 }
 
 pub fn now_rfc3339() -> String {