Add living workspace checks to continuity validation

[8Dionysus]

Summary

• add living-workspace continuity validator/test to the centralized continuity-context validation route
• leave the runtime-boundary route intact; it already includes the runtime-boundary bridge checks

Validation

• ok: Experience living workspace continuity runtime center contract is valid
• .................................................... [100%]
  52 passed in 0.39s
• [ok] Experience distillation validated: continuity-context
• ok: Experience runtime boundary bridge is valid
• .......... [100%]
  10 passed in 0.45s
• [ok] Experience distillation validated: runtime-boundary
• Markdown shape validation passed.
• [ok] mechanic artifact topology validated: experience
• [ok] validated mechanics topology: experience
• [ok] validated mechanic README cards: experience

Addresses PR #136 review threads: , .