feat(cli): comprehensive UX improvements for v3.5.0 (#7)

Implements 6-phase CLI UX improvement plan with comprehensive error handling, 
interactive features, and cross-platform consistency.

### Added
- Shell auto-completion (bash, zsh, PowerShell, Fish)
- Error codes (E101-E901) with documentation URLs
- Fuzzy matching "Did you mean?" suggestions (Levenshtein distance)
- Progress indicators (doctor [n/9] counter, GLMT proxy spinner)
- Interactive confirmation prompts with --yes/-y automation flag
- JSON output format (--json) for auth commands
- Impact display (session count, paths) before destructive operations
- Comprehensive test suite (15 tests, 100% pass rate)
- Complete error documentation in docs/errors/
- Cross-platform `--shell-completion` command

### Changed
- Error boxes: Unicode (╔═╗) → ASCII (===) for compatibility
- JSON output uses CCS version instead of schema version
- Help text includes EXAMPLES section across platforms
- Test suite properly counts test cases (not assertions)

### Fixed
- --yes flag bug (returned false instead of true)
- Help text consistency (added Uninstall section to bash)
- Test pass rate calculation (excludes skipped tests)
- Help section comparison (locale-specific sort)

### Testing
- 13/13 tests passing (2 legitimately skipped)
- Cross-platform verified (Node.js, bash, PowerShell)
- All error codes documented and tested

scripts/completion/ccs.bash

@@ -0,0 +1,81 @@
+# Bash completion for CCS (Claude Code Switch)
+# Compatible with bash 3.2+
+#
+# Installation:
+#   Add to ~/.bashrc or ~/.bash_profile:
+#     source /path/to/ccs/scripts/completion/ccs.bash
+#
+#   Or install system-wide (requires sudo):
+#     sudo cp scripts/completion/ccs.bash /etc/bash_completion.d/ccs
+
+_ccs_completion() {
+  local cur prev words cword
+  COMPREPLY=()
+
+  # Get current word and previous word
+  cur="${COMP_WORDS[COMP_CWORD]}"
+  prev="${COMP_WORDS[COMP_CWORD-1]}"
+
+  # Top-level completion (first argument)
+  if [[ ${COMP_CWORD} -eq 1 ]]; then
+    local commands="auth doctor"
+    local flags="--help --version -h -v"
+    local profiles=""
+
+    # Add profiles from config.json (settings-based profiles)
+    if [[ -f ~/.ccs/config.json ]]; then
+      profiles="$profiles $(jq -r '.profiles | keys[]' ~/.ccs/config.json 2>/dev/null || true)"
+    fi
+
+    # Add profiles from profiles.json (account-based profiles)
+    if [[ -f ~/.ccs/profiles.json ]]; then
+      profiles="$profiles $(jq -r '.profiles | keys[]' ~/.ccs/profiles.json 2>/dev/null || true)"
+    fi
+
+    # Combine all options
+    local opts="$commands $flags $profiles"
+    COMPREPLY=( $(compgen -W "${opts}" -- ${cur}) )
+    return 0
+  fi
+
+  # auth subcommands
+  if [[ ${prev} == "auth" ]]; then
+    local auth_commands="create list show remove default --help -h"
+    COMPREPLY=( $(compgen -W "${auth_commands}" -- ${cur}) )
+    return 0
+  fi
+
+  # Completion for auth subcommands that need profile names
+  if [[ ${COMP_WORDS[1]} == "auth" ]]; then
+    case "${prev}" in
+      show|remove|default)
+        # Complete with account profile names only
+        if [[ -f ~/.ccs/profiles.json ]]; then
+          local profiles=$(jq -r '.profiles | keys[]' ~/.ccs/profiles.json 2>/dev/null || true)
+          COMPREPLY=( $(compgen -W "${profiles}" -- ${cur}) )
+        fi
+        return 0
+        ;;
+      create)
+        # No completion for create (user enters new name)
+        return 0
+        ;;
+      list)
+        # Complete with list flags
+        COMPREPLY=( $(compgen -W "--verbose --json" -- ${cur}) )
+        return 0
+        ;;
+    esac
+  fi
+
+  # Flags for doctor command
+  if [[ ${COMP_WORDS[1]} == "doctor" ]]; then
+    COMPREPLY=( $(compgen -W "--help -h" -- ${cur}) )
+    return 0
+  fi
+
+  return 0
+}
+
+# Register completion function
+complete -F _ccs_completion ccs