chore: replace em dashes with hyphens, add no-em-dash rule to CLAUDE.md

CLAUDE.md

@@ -7,7 +7,7 @@ The private Go module every Vantage service imports. Extracted from the
 vantage-shared/
 ├── grpc/pb/                    # the agent↔control-plane wire types, hand-written
 ├── grpc/codec/                 # the JSON codec they travel over
-├── proto/vantage/v1/           # vantage.proto — documentation for the above
+├── proto/vantage/v1/           # vantage.proto - documentation for the above
 ├── mail/                       # the one email system: transport + templates
 ├── license/                    # payload, sign, verify, trusted keys, plans
 ├── models/                     # Instance, User, Settings
@@ -18,7 +18,7 @@ vantage-shared/
 └── cmd/lkctl/                  # issue and inspect licences by hand
 ```
 
-Module path is `gitea.hostxtra.co.uk/vantage/vantage-shared` — **lowercase
+Module path is `gitea.hostxtra.co.uk/vantage/vantage-shared` - **lowercase
 `vantage`**, though the Gitea org is canonically `Vantage`. Gitea serves both
 spellings; Go module paths are case-sensitive strings, and two spellings would
 cache as two modules. Keep the lowercase one.
@@ -46,7 +46,7 @@ v0.2.0`. Consumers pin exact versions.
 `grpc/codec`. Nothing generates them, and `vantage.proto` is not compiled by any
 build. It is the readable statement of the wire contract, and it lives in the
 same repository as the Go types precisely so that a message added to one can be
-added to the other **in the same commit** — that co-location is the only thing
+added to the other **in the same commit** - that co-location is the only thing
 enforcing the match, so do not split them again.
 
 There used to be two copies of `pb`, in the agent and the server, and they had
@@ -57,7 +57,7 @@ sides. The agent links the server half as dead code, which the linker drops.
 **A wire change lands in three steps, in this order**: release this module, bump
 the pin in `vantage/server` (live at the next push to main), bump the pin in
 `vantage/agent` (live only at the next `agent/v*` tag). The control plane will
-be ahead of the fleet in between, which was true before too — it is just written
+be ahead of the fleet in between, which was true before too - it is just written
 down in two `go.mod` files now instead of implied by a shared directory.
 
 ## Things that mirror something outside this repository
@@ -71,7 +71,7 @@ with a file in another repository:
   probe finds no ciphertext and reports "this database stores no ciphertext
   yet", so the one gate that catches what a key fingerprint cannot becomes a
   no-op. `settings` is deliberately in neither that map nor
-  `CiphertextCollections()` — its ESO read token is a SHA-256 hash, not
+  `CiphertextCollections()` - its ESO read token is a SHA-256 hash, not
   ciphertext.
 - **`mail/templates/layout.html.tmpl`** carries the control plane's dark theme
   values as **literal hex**. Email clients support neither `var()` nor a
@@ -81,8 +81,12 @@ with a file in another repository:
 - **`provision`** is the single implementation of the slug rules that both the
   control plane and Vantage HQ depend on. It is the one place those two
   repositories must agree on behaviour, which is why it is here rather than
-  copied — but it now also means a change to it is a release and two pin bumps.
+  copied - but it now also means a change to it is a release and two pin bumps.
 
 `mail/render_test.go` renders every template and fails if one exists that no
 case covers. The templates are parsed in `init()`, so without that test a
 mistyped field is a boot-time panic in three services.
+
+## Writing style
+
+Never use em dashes (the long dash character) anywhere: code, comments, UI copy, docs, commit messages. Use a plain hyphen ` - `, a comma, a colon, or split the sentence instead.