v0.1.0.0 feat: multi-store support (EGB-281) (#1)

* feat: multi-store support via .secrets-store + --store flag

Layer four-rule store resolution on top of the existing SECRETS_DIR primitive
so users can manage multiple isolated encrypted stores (work vs personal,
per-client, etc.) without giving up the tool's small-bash-script pitch.

Resolution order (highest first):
  1. --store <dir>  flag (parsed in main pre-pass)
  2. .secrets-store file in cwd or any ancestor up to $HOME
  3. SECRETS_DIR    env var (legacy escape hatch)
  4. ~/.secrets     default

resolve_store() updates both SECRETS_DIR and KEY_FILE so existing single-store
codepaths just work. New cmd_which / where / status report the active store.
cmd_init, push, pull, push_workspaces, pull_workspaces, list, rm, rekey, run,
which all call resolve_store at entry.

Hardening from the EGB-281 adversarial review:
- F1: cmd_run EXIT trap is now a named function (not string-interpolated),
  so paths with apostrophes still get plaintext cleaned up
- F2: symlinked .secrets-store files are skipped, never read
- F3/F4: --store flag rejects flag-shaped values and empty --store=
- F5: HOME unset is detected up-front with a directed error
- F11: check_initialized / check_key give context-aware errors that name
  both recovery paths (git clone vs secrets init) when a teammate clones
  a project bound to a non-existent store on their machine

Tests: 37 → 66 (29 new). HOME=\$TEST_TMPDIR added to test setup so the
walk-up logic stays bounded inside fixtures.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* docs: add Multiple stores section to README

Five subsections walk users through: how store resolution works, how to
set up a second store on a machine, how to bind a project, how teammates
join a bound project, and how to undo or change a binding. SECRETS_DIR
table entry now points readers at the new --store flag and .secrets-store
file as the preferred mechanisms.

* chore: bump version and changelog (v0.1.0.0)

First formal release. EGB-281 adds multi-store support; this commit
seeds the VERSION file (4-digit MAJOR.MINOR.PATCH.MICRO) and the
CHANGELOG.md.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

VERSION

@@ -0,0 +1 @@
+0.1.0.0