chore(release): 0.3.0

Bump workspace version 0.2.0 → 0.3.0.

CHANGELOG: documents the additions in this release —
  - `journal` Cargo feature with full TraceEvent enum + machine API
  - root state targetable by chart name
  - 113 deterministic-flow tests
  - verification/ workspace member with mechanical Creusot proofs
  - docs/002 formal semantics doc
  - README "How a chart behaves" building-block section
  - mise + just tooling overhaul (set shell, set script-interpreter)

README: integrates the semantics from docs/002 as eight building-
block rules that build on each other (active path, default-descent,
event bubbling, transitions, up-transition rule, entry/exit
ordering, timer lifecycle, emit / during / termination). Adds an
explicit "what hsmc deliberately does NOT have" table with what to
use instead. New "Verification" section pointing at `just verify`.

No behavior changes for v0.1 / v0.2 charts — every existing chart
compiles unchanged.

Cargo.toml

@@ -3,7 +3,7 @@ resolver = "2"
 members = ["hsmc", "hsmc-macros", "verification"]
 
 [workspace.package]
-version = "0.2.0"
+version = "0.3.0"
 edition = "2021"
 license = "MIT OR Apache-2.0"
 authors = ["Stephen Waits <steve@waits.net>"]