chore(hygiene): drop phantom README.md from cabal + dead .hypatia-ignore entry (#44)

## What

Two safe cleanups surfaced by the Hypatia-findings review (the
unambiguous, non-licence ones):

1. **`casket-ssg.cabal`** — removed `README.md` from
`extra-source-files` (only `README.adoc` exists). Clears the `File
listed in casket-ssg.cabal file does not exist: README.md` build
warning.
2. **`.hypatia-ignore`** — removed the dead
`cicd_rules/banned_language_file:examples/SafeDOMExample.res` exemption;
that `.res` fixture was deleted in #38, so the line no longer matches
anything. Kept the format header.

## Deliberately *not* in this PR

- **No SPDX/licence changes.** The findings review indicates the bulk of
the 18 are **missing-SPDX** on ~7 files (`templates/modern.css`,
`locales/*.txt`, `examples/web-project-deno.json`,
`config.example.yaml`). Per the estate's highest-priority guardrail (no
bulk SPDX sweeps; licence findings are flag-only, owner-approved
per-file), these are **held for owner approval**, not touched here.
- **No `http://` edits.** The two flagged `http://` in
`src/CasketGnosis.hs` are XML *namespace* URIs (sitemap / Atom) that
must remain `http://`; they belong in `.hypatia-ignore`, pending the
exact rule-id.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01WN6nPWWe4dvXfoqBG6auWN

---
_Generated by [Claude
Code](https://claude.ai/code/session_01WN6nPWWe4dvXfoqBG6auWN)_

Co-authored-by: Claude <noreply@anthropic.com>

Author: hyperpolymath

.hypatia-ignore

@@ -8,15 +8,6 @@
 # Comment lines (`#`) and blank lines are tolerated because they never
 # match the `rule:path` shape under -xF.
 #
-# ─── Example/documentation .res fixtures ────────────────────────────
-#
-# examples/SafeDOMExample.res is a DOCUMENTATION FIXTURE showing how to
-# consume the SafeDOM library from ReScript. The estate banned-language
-# rule correctly flags `.res` files everywhere — exempt this specific
-# documentation example so the governance gate passes on every PR.
-#
-# Going forward: this example should eventually be ported to
-# AffineScript (per the 2026-05-25 estate policy refresh —
-# `feedback_estate_lang_policy_2026_05_25`). When ported, drop this
-# line.
-cicd_rules/banned_language_file:examples/SafeDOMExample.res
+# (No active exemptions. The former
+# `cicd_rules/banned_language_file:examples/SafeDOMExample.res` exemption
+# was removed after that .res fixture was deleted in #38.)

casket-ssg.cabal

@@ -13,7 +13,6 @@ copyright:          2024-2026 Jonathan D.A. Jewell
 category:           Web
 build-type:         Simple
 extra-source-files: README.adoc
-                    README.md
 
 executable casket-ssg
     main-is:          CasketGnosis.hs