fix: use VT100 box-drawing characters and semantic colors for output

[rsnodgrass]

Summary

• Replace ASCII |--- and | with VT100 box-drawing characters (├──, └──, │) in tree output for crisp rendering
• Fix tree continuation lines: last siblings now use └── and omit the vertical bar below terminal nodes
• Add space after tree connectors and before action suffixes (name (+) instead of name(+)) for readability
• Table output uses box-drawing characters (│, ─, ┼) instead of +, -, | for non-markdown mode
• Add semantic colors to table rows: green (add), red (delete), yellow (update), magenta (recreate), cyan (import/moved)
• Colors respect NO_COLOR env via the fatih/color library (already a dependency)
• Markdown output unchanged

Before / After

Tree

Before:

|---github_repository
|       |---terraform_plan_summary(+)
|---module
|       |---github["demo-repository"]
|       |       |---github_branch

After:

├── github_repository
│   └── terraform_plan_summary (+)
└── module
    └── github["demo-repository"]
        ├── github_branch

Table

Before:

+------------+---------------------------+
|   CHANGE   |         RESOURCE          |
+------------+---------------------------+
| add (1)    | aws_instance.example1     |
+------------+---------------------------+

After (with semantic colors):

┼────────────┼───────────────────────────┼
│   CHANGE   │         RESOURCE          │
┼────────────┼───────────────────────────┼
│ add (1)    │ aws_instance.example1     │  ← green
┼────────────┼───────────────────────────┼
│ delete (1) │ aws_instance.example2     │  ← red
┼────────────┼───────────────────────────┼

graph LR
    A[writer/tree.go] -->|"├── └── │"| B[Crisp tree lines]
    C[writer/table.go] -->|"│ ─ ┼ + Rich()"| D[Box-drawing + colors]
    E[tree/tree.go] -->|"AddChild spacing"| F[Drawable tree spacing]
    B --> G[Better terminal output]
    D --> G
    F --> G

Loading

Test plan

• All existing tests updated and passing (go test ./...)
• Verify tree output in terminal with a real Terraform plan
• Verify table output renders correctly with colors in terminal
• Confirm markdown output is unaffected
• Verify NO_COLOR=1 disables table colors

Co-Authored-By: SageOx ox@sageox.ai