refactor: reduce cyclomatic complexity in high-complexity functions

[leonardomso]

Summary

Refactored 4 functions flagged by gocyclo for exceeding the complexity threshold of 15, improving code maintainability and readability.

Complexity Reductions

Function	Before	After	Improvement
runCheck()	26	~7	73% reduction
outputText()	20	~7	65% reduction
Format()	20	~4	80% reduction
FindFixes()	17	~5	71% reduction

Changes

cmd/check.go - runCheck() (26 → ~7)

• Extract exitOnError() for consistent error handling
• Extract scanFiles() for file scanning phase
• Extract parseAndFilterLinks() for parsing phase
• Extract checkLinks() for URL checking phase
• Extract routeOutput() for output routing

cmd/check_output.go - outputText() (20 → ~7)

• Extract printSummaryLine() for summary output
• Extract getEmptyResultsMessage() for empty state handling
• Extract shouldGroupResults() for display mode decision
• Extract outputGroupedResults() and outputFlatResults()
• Extract maybeShowIgnored() for conditional ignored display

internal/output/markdown.go - Format() (20 → ~4)

• Extract writeHeader() for report header
• Extract writeSummaryTable() for summary stats
• Extract writeDeadLinksSection() with table and details helpers
• Extract writeWarningsSection() with table and redirect details
• Extract writeDuplicatesSection() for duplicates table
• Extract writeIgnoredSection() for ignored URLs
• Use fmt.Fprintf() instead of b.WriteString(fmt.Sprintf())

internal/fixer/fixer.go - FindFixes() (17 → ~5)

• Extract buildURLToLinksMap() for URL lookup map creation
• Extract isFixableRedirect() for eligibility check
• Extract addOrUpdateFix() for fix map management
• Extract createFix() for fix object creation
• Extract applyRefInfo() for reference info detection

Testing

• All 197 tests passing
• 0 linter issues
• Verified with gocyclo -over 15 . - no flagged functions from original scope

Go Report Card

This PR addresses the gocyclo warnings from Go Report Card, improving the project's code quality score.