fix: change const to let for variables that get reassigned

[dspearson]

Problem

The package fails to run with Bun due to const reassignment violations. Bun properly enforces const semantics, causing runtime errors when const-declared variables are reassigned.

Error example:

803 |           swarmPrompt = enhanceSwarmPrompt(swarmPrompt, maxAgents);
                ^
error: This assignment will throw because "swarmPrompt" is a constant
    at /tmp/bunx-1000-claude-flow@alpha/node_modules/claude-flow/src/cli/simple-commands/swarm.js:803:11

381 |       const swarmPrompt = `You are orchestrating a Claude Flow Swarm using Claude Code's Tas
                  ^
note: The symbol "swarmPrompt" was declared a constant here:
   at /tmp/bunx-1000-claude-flow@alpha/node_modules/claude-flow/src/cli/simple-commands/swarm.js:381:13

Solution

Changed const to let for three variables that get reassigned later in the code:

1. swarmPrompt (swarm.js:381) - reassigned when memory protocol enhancement is enabled via --claude flag
2. isAvailable (coordination.js:58) - reassigned in error catch block during ruv-swarm fallback
3. hiveMindPrompt (hive-mind.js:2009) - reassigned when memory protocol enhancement is enabled via --claude flag

Testing

✅ Verified with both package runners:

• npx "dspearson/claude-flow#fix/bun-const-reassignment" --help ✅ Works
• bunx "dspearson/claude-flow#fix/bun-const-reassignment" --help ✅ Works (previously failed)

Impact

• Compatibility: Fixes runtime errors in Bun
• Scope: Minimal - only changes variable declarations, no logic changes
• Risk: Very low - let is functionally identical to const when variables are reassigned