feat(cfl): port config show/test/clear commands

[rianjs]

Port config management commands from confluence-cli PR #106.

Files to create:

• tools/cfl/internal/cmd/configcmd/config.go - Parent command
• tools/cfl/internal/cmd/configcmd/show.go - Display config with masked tokens
• tools/cfl/internal/cmd/configcmd/test.go - Test connectivity
• tools/cfl/internal/cmd/configcmd/clear.go - Remove config file
• Tests for each

Commands:

cfl config show:

• Masked tokens (first 4 + last 4 chars)
• Source indicators (env var name, config file, or "not set")

cfl config test:

• Test connectivity with clear error messages

cfl config clear:

• Remove config file with note about active env vars

Source: open-cli-collective/confluence-cli#106

[rianjs]

Implementation Plan

Files to create:

• tools/cfl/internal/cmd/configcmd/config.go - Parent command
• tools/cfl/internal/cmd/configcmd/show.go - Display config with masked tokens
• tools/cfl/internal/cmd/configcmd/test.go - Test connectivity
• tools/cfl/internal/cmd/configcmd/clear.go - Remove config file
• Tests for each

Commands:

cfl config show:

• Display current configuration
• Masked tokens (first 4 + last 4 chars)
• Source indicators (env var name, config file, or "not set")

cfl config test:

• Test connectivity using current credentials
• Clear pass/fail with troubleshooting suggestions

cfl config clear:

• Remove config file
• Note about active env vars still being used

Register in main.go:

• Add configcmd.Register to the command list