fix(tiff): add missing tag names and value decoding

[rpuneet]

Summary

• Add proper names for 5 standard TIFF 6.0 tags that were displaying as hex IDs
• Add enum value decoding for tags with known value meanings

Tags Added

Tag ID	Name	Values
0x010A	FillOrder	Normal, Reversed
0x0129	PageNumber	(no decoding needed)
0x013D	Predictor	None, Horizontal differencing, Floating point predictor
0x0152	ExtraSamples	Unspecified, Associated Alpha, Unassociated Alpha
0x0153	SampleFormat	Unsigned integer, Signed integer, IEEE floating point, Undefined

Test plan

• Unit tests for new tag names in lookup_test.go
• Unit tests for enum value decoding in values_test.go
• All existing tests pass (go test ./...)

Fixes #39

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[rpuneet]

Code Review: APPROVED

Clean implementation adding 5 missing TIFF 6.0 tags with proper enum value decoding:

• FillOrder (0x010A): Normal, Reversed
• PageNumber (0x0129): Name only (no decoding needed)
• Predictor (0x013D): None, Horizontal differencing, Floating point predictor
• ExtraSamples (0x0152): Unspecified, Associated Alpha, Unassociated Alpha
• SampleFormat (0x0153): Unsigned integer, Signed integer, IEEE floating point, Undefined

Tests comprehensive. CI passes. Follows existing patterns.

Fixes #39