repository: honor --dry-run in repository delete

[jonathanmcmichael]

What

lore repository delete --dry-run now actually performs a dry run instead
of deleting the repository. The CLI also reports "Repository would be
deleted" rather than "Repository deleted successfully" when --dry-run is
set.

Why

lore-revision/src/repository/delete.rs::delete() never checked
dry_run — it called repository_service.delete(id) unconditionally.
Every other destructive command in this codebase (revision commit,
branch push/switch, clone) gates its mutating call behind
globals.dry_run() / execution_context().globals().dry_run(); delete
was simply missing that check. This is a safety-flag correctness bug: a
user relying on --dry-run before a destructive operation gets no warning
and no protection.

How

• lore-revision/src/repository/delete.rs: wrap the
  repository_service.delete(id) call in
  if !execution_context().globals().dry_run(), following the same pattern
  already used in repository/clone.rs and branch/push.rs in this crate.
  The repository name/ID is still resolved and validated either way, so a
  dry run still surfaces a bad URL/name the same way a real delete would.
• lore-client/src/cli/commands/repository.rs: the delete callback's
  success message now distinguishes dry_run (prints "Repository would be
  deleted") from a real delete ("Repository deleted successfully"),
  matching the message style already used by revision commit
  ("Previewing commit" vs "Committing").

Testing

• cargo +nightly fmt --all
• cargo clippy -p lore-revision -p lore-client --all-targets -- -D warnings --no-deps (full-workspace clippy currently fails on an unrelated pre-existing issue in lore-revision/src/util/fs.rs, not touched by this PR)
• cargo test -p lore-revision -p lore-client
• No test included in this PR. There was no existing test coverage for
  repository delete at all, and none of this crate's tests spin up a
  real server, so covering this properly meant adding new test
  infrastructure rather than a single test function. That's split out
  into a companion PR (in-process gRPC server harness + dry-run/real-delete
  tests for repository::delete::delete()) so it can be reviewed on its
  own.

Notes for reviewers

Small, mechanical, non-security change — no auth/crypto paths touched.

AI assistance disclosure

This change (code and this PR description) was developed with Claude (Anthropic) assistance. I reviewed and tested the change myself and am responsible for its correctness.