docs(changelog): structure [Unreleased] with Added/Changed/Fixed/Deferred subsections

Adds a `### Deferred` subsection to CHANGELOG.md's `[Unreleased]`
entry, immediately after the existing `### Removed` subsection,
documenting per-plugin `screen.py` helper duplication
(`_safe_str`, `_decode_bytes`, `_load_bundle`, etc.) as
intentional technical debt deferred pending broader empirical
experience across diverse corpora.

Wording is verbatim from CONV7_handoff.md sec 5.5: "Verbatim. Do
not paraphrase. This entry is documented technical debt - the
wording is the contract Conv 1 negotiated, and downstream readers
(reviewers, future maintainers) will compare it to whatever the
future Conv 11+ commit ends up doing."

The [Unreleased] entry now structures all five Keep-a-Changelog
buckets relevant to this revision arc: Added, Changed, Fixed,
Removed, Deferred. The `Deferred` bucket is non-standard but
explicit and useful here: it documents work that would be
in-scope for a future revision but is intentionally NOT in the
present release. Reviewers see (1) what changed, (2) what didn't
change but probably should, and (3) why the second list isn't a
silent omission.

NOT MODIFIED:

  * The `[Unreleased]` header itself remains as `[Unreleased]`.
    Renaming to `[3.1.0] - YYYY-MM-DD` is Conv 10's release-dance
    work, not Conv 7's. The version-match xfail in
    test_metadata.py will continue to xfail until Conv 10 cuts
    the tag and adds a matching `[3.1.0]` Released entry.
  * The `[3.0.1] - 2026-04-04` Released entry is unchanged.
  * No code, no plugins, no tests modified. The metadata
    consistency test count remains 103 passed + 1 xfailed.

ARC NOTE:

This is the FINAL commit in the Conv 7 revision arc, completing
the §10 acceptance gate:

  ✓ 6 commits on top of c80753e (C0..C6)
  ✓ CI live and green on Windows + all of {Ubuntu 22.04, 24.04,
    macOS 14}, well above the §10 minimum
  ✓ README has live GitHub Actions CI badge
  ✓ Configurable temperature works end-to-end (EL + IL)
  ✓ tests/test_metadata.py with 2 regression assertions
  ✓ README has "Using local LLM providers" section
  ✓ CHANGELOG [Unreleased] has Added/Changed/Fixed/Deferred
    subsections (THIS COMMIT)
  ✓ All six pre-commit gates pass
  ✓ Manual GUI smoke completed on C2, C3
  ✓ audit_decorators clean across the arc
  ✓ PROMPT_VERSION strings unchanged (Conv 6 byte-identity
    goldens still pass)

After CI #6 confirms green, the Conv 7 to Conv 1 status report
will be drafted per sec 13, and Conv 8 (Reviewer 1's compulsory
items: LLM evaluation methodology, fuller installation/usage
docs) can begin.

Spec: see CONV7_handoff.md sec 5.5 (verbatim wording, do not
paraphrase) and sec 7 commit table row 6.

Author: normand-marineau

CHANGELOG.md

@@ -31,6 +31,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `plugins/_parking_lot/` (historical drafts folder, retained in git history)
 - Timestamped backup `.py` files in `prisma_hub/` and `plugins/*/` directories
 
+### Deferred
+
+- Per-plugin `screen.py` files contain stage-tuned copies of helpers
+  (`_safe_str`, `_decode_bytes`, `_load_bundle`, etc.) that overlap
+  with `plugins/_common/` versions. Substitution would require a
+  unified `_common/parser.py` + `_common/bundle.py` whose behavior
+  preserves all four stages' (EH, IH, EL, IL) byte-identity goldens
+  simultaneously. Deferred pending broader empirical experience
+  across diverse corpora.
+
 ## [3.0.1] - 2026-04-04
 
 Initial GitHub-tagged release. See https://github.com/lars-ulaval/metaScreener/releases/tag/v3.0.1