Refresh Spec Kit scaffolding to CLI 0.14.3

[mnriem]

Regenerates this repo's CLI-generated Spec Kit tooling in place using specify 0.14.3 (integration=copilot, script=sh, --skills), and updates the docs so every documented CLI command line matches 0.14.3.

Previous version: unknown — legacy scaffold with no .specify/init-options.json. init-options.json now records "speckit_version": "0.14.3".

Command files changed (layout migration):

• Commands moved from .github/agents/speckit.*.agent.md + thin .github/prompts/speckit.*.prompt.md pointers → .github/skills/<name>/SKILL.md (analyze, checklist, clarify, constitution, converge, implement, plan, specify, tasks, taskstoissues).
• Removed the now-orphaned old .github/agents/speckit.*.agent.md and .github/prompts/* files.
• Kept .github/agents/copilot-instructions.md — still the Copilot agent-context target for the current CLI and holds feature data.

Also refreshed:

• .specify/scripts/bash/* (check-prerequisites, common, create-new-feature, setup-plan) + new setup-tasks.sh
• .specify/templates/* (checklist, plan, spec, tasks)
• New .specify/{init-options,integration}.json, .specify/integrations/, .specify/workflows/

README.md documentation updates (match CLI 0.14.3):

• Init flag change: specify init . --ai copilot → specify init . --integration copilot --integration-options="--skills" (the --ai flag no longer exists in 0.14.3).
• Slash-command names: dot-style speckit.<x> → hyphenated Copilot skill slash commands /speckit-<x> throughout (table + each step reference).
• Step 5 usage now describes invoking /speckit-* slash commands in Copilot Chat instead of selecting an "Agent" from a dropdown.
• Added the new /speckit-converge command to the command table.
• Narrative prose, screenshots, and app-specific content left intact.

No preset or extensions were present previously, so none were reinstalled. No application source or specs/ content was modified — changes are confined to Spec Kit scaffolding plus the README doc corrections.