Release v0.5.0

[jamiesun]

Version bump to v0.5.0 (minor; pre-1.0).

Changes since v0.4.0

• wasm host W0-W4: integer interpreter, minimal WASI preview1, static type validation, float execution + robustness suite ([wasm] Add W0 scoot-wasm bytecode host #145, feat(wasm-host): W1 integer interpreter for scoot-wasm #147, feat(wasm-host): W2 minimal WASI preview1 subset for scoot-wasm #148, feat(wasm-host): add W3 type validation pass #149, wasm: complete W4 (float execution + malformed-module robustness suite) #162)
• feat: wasm_tool action for compute-only Wasm packages (feat: add wasm_tool action for compute-only packages #154)
• wasm: narrow plugin sandbox to stdin/stdout/stderr/argv as a new hard rule (wasm: narrow plugin sandbox to stdin/stdout/stderr/argv (new hard rule) #164)
• feat: committed playground/ test environment with full action coverage (feat: add committed playground test environment with full action coverage #161)
• release: single ReleaseSafe flavor, ship scoot-wasm artifacts, add Homebrew tap (release: single ReleaseSafe flavor + ship scoot-wasm + Homebrew tap #166)
• fix(release): reference SCOOT_DOCKERHUB_* secrets so the Docker Hub login step actually runs
• docs: README rewrite + isometric infographic, English comment translation (docs: rewrite README to be human-friendly and concept-first #160, docs: refresh README infographic with isometric hero image #165, [docs] Remove README language link #146, chore: translate Chinese comments and strings to English #153)

Bump level minor (multiple new capabilities, no breaking change). Tag v0.5.0 will be pushed after merge to trigger the Release workflow.